The 500-kilogramme (1,100-pound) German bomb was discovered early on Sunday morning in King George V Dock, during planned works near the runway of London's most central airport.

As experts worked to move the unexploded ordnance, the airport was shut down and a 214-metre exclusion zone was initially imposed which prompted the evacuation of up to 500 residents.

While they were allowed to return to their homes on Monday evening, locals were evacuated from another area after the 1.5-metre (five-foot) shell was moved within the dock.

"While every effort is being made to progress the operation as quickly as possible, it is important that all of the necessary steps and precautions are taken to ensure it is dealt with safely," London's Metropolitan Police said late Monday.

Those within the new exclusion zone were asked by the Newham Council local authority to stay with family or friends on Monday evening, although a rest centre was also established.

Removal of the fused device depends on the tides, with naval and police experts having to wait until close to midnight (0000 GMT) before they can transport the bomb further along the River Thames where it can safely be dealt with.

"We are taking the necessary steps to ensure the device is as safe as possible before we remove it from the sea bed and tow it away to a safe disposal site," said Jonny Campbell, the naval officer in charge of the bomb disposal divers.

"We will then attach high-grade military explosives before carrying out a controlled explosion," he added.

Authorities said the operation would probably conclude overnight, while London City Airport chief executive Robert Sinclair said he expected the airport to be open as normal on Tuesday.

Monday's shutdown affected up to 16,000 passengers who were due to fly from London's fifth-biggest airport, although some airlines switched their flights to the city's other hubs.

London was heavily bombed during the "Blitz", the Nazi German air attacks of September 1940 to May 1941.

London City Airport opened in 1987 in the disused docklands. It handled 4.5 million passengers in 2017 and is mainly used by business travellers.