All flights at London City Airport have been disrupted after protesters gained access to the runway, BBC reports.
The Met Police said it was called to the site at about 05:40 BST after nine protestors "locked themselves together" on the runway.
The Black Lives Matter UK movement has confirmed it is responsible for the protest.
The airport said inbound flights were being diverted and it hoped to "resume operations as soon as possible".
Black Lives Matter UK said: "Whilst at London City Airport a small elite is able to fly, in 2016 alone 3,176 migrants are known to have died or gone missing in the Mediterranean.
"Black people are the first to die, not the first to fly, in this racist climate crisis.
It said it was investigating how the protesters had managed to get air-side - including the suggestion that they swam across the Thames or used a boat.
It added no arrests have been made at this stage.
City Airport is popular with bankers and business professionals due to its proximity to Canary Wharf in London Docklands.
Last year, a record 4.3 million passengers used the airport.