Police said that the ordnance was found during pre-planned work at the airport early on Sunday, and set up a 214-metre exclusion zone around the device that evening.
"All flights in and out of London City on Monday are cancelled and an exclusion zone is in place in the immediate area," said Robert Sinclair, CEO of London City Airport, the city's fifth biggest and most central airport.
The Metropolitan Police said that properties within the exclusion zone had been evacuated, and that a number of road cordons were in place.
Get the latest election news, live updates and election schedule for Lok Sabha Elections 2019 on ndtv.com/elections. Like us on Facebook or follow us on Twitter and Instagram for updates from each of the 543 parliamentary seats for the 2019 Indian general elections.