Navy divers are working to defuse a Second World War bomb which forced the closure of London City Airport and the evacuation of hundreds of homes.
The airport, in east London, has been shut all day, plunging 16,000 people into travel chaos as they are left unable to catch their flights.
Around 300 flights, in and out, were cancelled and the airport is not expected to reopen until Tuesday morning.
The 1,100lb bomb is ten times more powerful than those used by the London 7/7 attackers, according to a Royal Navy bomb expert.
Roads surrounding the airport have been closed and a 700-ft exclusion zone has been put in place, after the device was found at 5am on Sunday.
Up to 500 people have been evacuated from the surrounding area of Newham, but dozens of families have refused to leave their homes.
Royal Navy bomb squad officers speak to a diver in the water, just yards from the runway at London City Airport
Two Royal Navy bombsquad officers head out in a dinghy while a device is dealt with at George V Dock by London City Airport
Royal Navy bomb squad officers at the scene of the incident on George V Dock, at London City Airport, on Monday afternoon
The airport has been closed while the bomb squad officers (pictured) investigate at the scene following the major alert
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Andrew Scott, from City of London Airport said: 'We have been told by the Navy that it is somewhere in the region of a 1,100lb bomb, a significant size.
'The object was identified in the morning and over the course of the day the Royal Navy decided with the Metropolitan Police to establish a cordon.
'We are hoping it will be removed by tomorrow.'
Police said they were working with the Royal Navy to remove the device, which was discovered during work at George V Dock, yards from the end of the runway.
The 500 kilo bomb that has closed City airport will be dragged for nine hours underwater before it is detonated in a controlled explosion.
Police advise local residents at Galleon's Lock of the situation where an unexploded Second World War bomb has been discovered adjacent to London City Airport
Those residents based further away from the site are not being evacuated by the authoroties, but are advised to stay away
Bomb disposal experts from the British Army and the Royal Navy are working together to make the unexploded device safe
The 500 kilo bomb will be dragged for nine hours underwater before it is detonated in a controlled explosion
Royal Navy diving crews prepare in a dinghy close to the runway at City Airport in east London on Monday
Divers prepare to go into water by London City Airport as the Royal Navy bomb squad deals with a Second World War explosive
Security teams at London City Airport arrive at the scene as Royal Navy bomb squad teams deal with the incident
People with luggage walk away from the cordon around London City Airport after a number of roads were closed off today
In a statement, Scotland Yard said: 'The device has been examined by Met Police and Royal Navy dive teams and is confirmed as being a 1,100lb tapered-end shell, measuring approximately 5-ft.
'It is lying in a bed of dense silt and the first stage of the removal operation is to free the shell from the silt so that it can be floated for removal.
'The operation to remove the ordnance is ongoing in partnership with our colleagues in the Royal Navy.WW2 bomb is 'ten times that of 7/7 explosives'
Former Royal Navy Lt Cdr David Welch said German bombs are more dangerous than present-day explosives as they are an 'unknown danger' to bomb squads.
Mr Welch said: 'British and German bombs are more dangerous now than when they were first dropped, these items have been armed.
'It is what we call blind because it has not functioned as intended but it is perfectly functional.
'We never find a bomb which no longer has the oomph it did when it was dropped.
'The danger it is presenting is unknown, but it's not going to go off on its own, you have to do something to it, if you do not touch it, it won't go off.
'The Navy tend to drag them out by hand and put a strap around it and relocate it out to a safer area.
'Water has a great dampening effect to the fragmentation.
'So being underwater is far better than someone's garden, but still at the bottom of the Thames you are going to get a fairly hefty noise and spray but not too much fragmentation.
'Windows that are nearby could be broken and as it's on the seabed there is a risk of ground shock.
'They are moving it because of all the associated risks.'
Mr Welch added: 'It's still quite big, the 7/7 bombs were 5kg so it is bigger than those.
'It's quite a straight forward process, we do these about 20 or 30 times a year and the military do it quite a lot, it is one of those things where knowledge is definitely power.
'It can still bite you if you do not act in an appropriate way and you could do something that could cause it to function.
'But these divers can literally do it with their eyes closed.'
'The timing of removal is dependent on the tides, however, at this stage we estimate that the removal of the device from location will be completed by tomorrow morning.'
Robert Sinclair, CEO of London City Airport, confirmed it would remain closed for the rest of Monday.
During the Blitz some 30,000 tonnes of explosive were dropped across London, usually set to go off immediately, on a timer or booby trapped.
Unexploded devices are known among experts as 'blind' and teams will dig around the shell before attaching a strap and relocating it to a safer area.
The water will absorb much of the force, but if the bomb went off in King George V dock it could still cause a significant amount of spray, noise and potentially damage to nearby homes by smashing windows.
Later this afternoon and this evening Royal Navy experts are planning on removing the shell out to the Thames Estuary before disposing of it.
It is hoped that evacuated residents will be able to go back home this evening and City Airport will reopen as usual on Tuesday.
Newham Council have confirmed that 'Officers are assisting with a controlled evacuation of up to 500 people.'
Streets in the exclusion zone include, Holt Road, Leonard Street, Lord Street, Newland Street, Tate Road, Muir Street and Kennard Street.
A spokesman added that a former town hall building had been opened up for evacuees.
'Work will not start on lifting and removing the device until the initial 700-ft zone is clear', he said.
'When work starts to remove it, it is expected the exclusion zone will be extended to 820-ft and more properties will need to be evacuated.'
Carriers using London City include British Airways, Lufthansa Flybe, CityJet and KLM.
Four-and-a-half million passengers used London City last year and around 50 routes are now served.
Due to its central Location, the airport is popular with business-people heading to destinations around Europe.
BA said it was doing 'everything possible to minimise disruption for our customers', but added the closure of the airport was 'beyond our control'.
While CityJet tweeted: 'Please note our flights are not cancelled. These have been rescheduled to and from Southend for any updates please see our website.'
Flybe said customers could rebook any 'disrupted flights' via their website.
Adding: 'If you have an onward connection please check the information for all separate flights individually.'
Lufthansa confirmed that its four flights scheduled for today were cancelled, with passengers automatically booked onto flights out of London Heathrow.
A spokesman added: 'We regret the inconvenience caused to the affected passengers, safety has the highest priority at Lufthansa.'
Police stand on guard outside London City Airport after a 700-ft exclusion zone was set up following the alert
Police officers have a meeting outside a cordon with residents around London City Airprot evacuated from their homes
London City Airport, to the east of the capital's financial district, sits on the banks of the River Thames (pictured)
Transport for London (TfL) said Docklands Light Railway services will not run between Pontoon Dock and Woolwich Arsenal (pictured, London City Airport DLR station is cordoned off)
Transport for London (TfL) said Docklands Light Railway services will not run between Pontoon Dock and Woolwich Arsenal.
Police have since set up a small tea and coffee stand for locals who have refused to leave their homes, but officers have warned that if anyone goes beyond the cordon they may not be allowed back.
Local resident Amanda Hawkins, 53, said: 'They knocked on my door at 6am and said they had found a bomb and that you're strongly advised to evacuate.
'But they can't make you, so I'd rather just stay at home. I've lived here most of my life since I was 12. I'm not leaving.'
Jean Lee, 55, was awoken at 1am by police who wanted to evacuate her to Stratford, but has also refused to leave.
Her son Blazej Zdanowicz, 35, lives nearby and came to check how she was getting on.
A police officer inspects the cordon near London City Airport today after a 700-ft exclusion zone was set up
Planes are left parked on the runway at London City Airport today after the runway closed
A 700-ft exclusion zone was set up after the bomb was found at King George V Dock (shown on map). The bombsite is just yards away from London City Airport's runway
Outside her home, he said: 'They came at 1am but mum decided to stay, they are taking people to Stratford and my mum was very concerned about it last night, it's very serious stuff but she would rather stay at home than move.'
Michelle Goodwin, 35, told police she would not move unless she would be accompanied by her dog, two cats and two rabbits.
Outside her home she said: 'If my animals are going too, then i'm going, if it goes off it goes off.
'It's all over the top, what a waste of resources.'
The Metropolitan Police confirmed officers were 'responding to a World War Two ordnance in the River Thames at George V Dock'.
Airport CEO Robert Sinclair said: 'I urge any passengers due to fly today not to come to the airport and to contact their airline for further information.
'All flights in and out of London City on Monday are cancelled and an exclusion zone is in place in the immediate area.
'I'm pleased to say some airlines were able to secure space at alternative airports so that some flights can operate.
'Thanks to those airports, CityJet at Southend Airport and Alitalia at Stansted Airport for stepping in to help out.
'I recognise this is causing inconvenience for our passengers, and in particular some of our local residents.
'The airport is cooperating fully with the Met Police and Royal Navy and working hard to safely remove the device and resolve the situation as quickly as possible.
'The operation is proceeding well and we anticipate it to be completed during the course of this evening.
'At this stage we fully expect that the airport will be open as normal tomorrow.'
He added: 'Passengers due to travel on Tuesday are asked not to arrive more than two hours before their flight.'
Due to its central Location, the airport is popular with business-people heading to destinations around Europe
Four-and-a-half million passengers used London City last year and around 50 routes are now served
A spokesman added: 'The ordnance was discovered as part of pre-planned work at London City Airport and reported to the police at 5:06am on Sunday, 11 February.
'Specialist officers and the Royal Navy have attended and confirmed the nature of the device.
'The operation to remove the ordnance is ongoing in partnership with our colleagues in the Royal Navy.
'At 10pm, an operational decision was made with the Royal Navy to implement a 214m (230 yard) exclusion zone to ensure that the ordnance can be safely dealt with whilst limiting any risk to the public.
'There will also be disruption to inbound and outbound flights during the operation. London City Airport are urging passengers to contact their airline before travelling.'
The closure comes as London City Airport plans its £400million redevelopment project (pictured, an artist's impression of the airport's new terminal)
City Airport plans to extend its terminal to accommodate more passengers, build seven new aircraft stands and create a parallel taxiway to boost runway capacity (pictured, an artist's impression of the new airport)
TfL tweeted the airport was shut and said road closures were in effect.
'The airport has been closed due to an emergency services incident. There are also additional local road closures due to the incident. Traffic is light in the area', a spokesman said.
The closure comes as London City Airport plans its £400million redevelopment project.
The privately-funded scheme includes extending the terminal to accommodate more passengers, building seven new aircraft stands and creating a parallel taxiway to boost runway capacity.
Two million more passengers per year will be able to use to use the airport from 2025, with 30,000 additional flights annually.Where did the German bombs fall during the Blitz? Interactive map plots out the most intense bombing campaign that Britain has ever seen
A boy retrieves an item from a rubble-strewn street after German bombing raids in the first month of the Blitz, September 1940
The Blitz began on September 7, 1940, and was the most intense bombing campaign Britain has ever seen.
Named after the German word 'Blitzkrieg', meaning lightning war, the Blitz claimed the lives of more than 40,000 civilians.
Between September 7, 1940, and May 21, 1941, there were major raids across the UK with more than 20,000 tonnes of explosives dropped on 16 British cities.
London was attacked 71 times and bombed by the Luftwaffe for 57 consecutive nights.
The City and the East End bore the brunt of the bombing in the capital with the course of the Thames being used to guide German bombers. Londoners came to expect heavy raids during full-moon periods and these became known as 'bombers'moons'.
More than one million London houses were destroyed or damaged and of those who were killed in the bombing campaign, more than half of them were from London.
In addition to London's streets, several other UK cities - targeted as hubs of the island's industrial and military capabilities - were battered by Luftwaffe bombs including Glasgow, Liverpool, Plymouth, Cardiff, Belfast and Southampton and many more.
Deeply-buried shelters provided the most protection against a direct hit, although in 1939 the government refused to allow tube stations to be used as shelters so as not to interfere with commuter travel.
However, by the second week of heavy bombing in the Blitz the government relented and ordered the stations to be opened. Each day orderly lines of people queued until 4pm, when they were allowed to enter the stations.
Despite the blanket bombing of the capital, some landmarks remained intact - such as St Pauls Cathedral, which was virtually unharmed, despite many buildings around it being reduced to rubble.
Hitler intended to demoralise Britain before launching an invasion using his naval and ground forces. The Blitz came to an end towards the end of May 1941, when Hitler set his sights on invading the Soviet Union.