A 500kg World War Two bomb has been found at George V Dock on Sunday during planned work at the east London airport.
The airport has been shut all day and all flights cancelled, affecting up to 16,000 passengers, officials said.
The airport said if the attempt to remove the device is successful all flights will run as normal on Tuesday.
Families in the area have been evacuated with the exclusion zone set to be widened when specialists from the Met Police and the Royal Navy begin removing the bomb.
The Royal Navy said it was taking the necessary steps to "ensure the device is as safe as possible" before removing it from the sea bed and towing it away to a safe disposal site.
According to the airport's website, a total of 261 arrivals and departures had been scheduled for Monday.
Passengers have been told not to travel to the airport as the terminal is closed and to contact their airline.
Among passengers affected were Tottenham Hotspur fans heading to Italy for a Champions League game against Juventus.
The north London club advised any fans flying to Milan to "contact their airline as soon as possible", ahead of the match in Turin on Tuesday.
