A Second World War ordnance has been discovered in the River Thames.
The device was found at George V Dock during work at London City Airport on Sunday morning.
Police have set up a 214-metre (700ft) exclusion zone and the airport remains closed.
Passengers due to fly on Monday are advised not to travel to the airport until further notice.
Specialist officers are working with the Royal Navy to remove the ordnance, the Metropolitan Police said.
A spokesman said on Sunday night: “At 10pm an operational decision was made with the Royal Navy to implement a 214-metre 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.”
A spokesman for the airport added: “All passengers due to travel from London City on Monday are advised to contact their airline for further information. Passengers are advised not to travel to the airport until further notice.”