Flights have been disrupted at London City Airport after a group of "Black Lives Matter" protesters forced their way and locked themselves together on the runway.

The protesters reportedly bypassed security by using a rubber dinghy to cross the docks.

Photographs on Twitter show the protesters surrounded by police and lying under a wooden tripod.

They had also erected two large posters with the slogans "Black Lives Matter" and "Climate Crisis is a Racist Crisis".

The British arm of the group, which started in the United States as a reaction to fatal shootings of black people by white U.S. police officers, said it wanted to highlight Britain's environmental impact on the lives of black people locally and globally.

"Black people are the first to die, not the first to fly, in this racist climate crisis," the group said.

"When black people in Britain are 28 percent more likely to be exposed to air pollution than their white counterparts, we know that environmental inequality is a racist crisis."

The campaign group, which blocked a main road to London's Heathrow Airport in August, said City airport was designed for the wealthy while those who lived near the site struggled on low salaries.

Meanwhile, police said they were negotiating with the protesters. "We are awaiting the arrival of specialist resources that are able to 'unlock' the protesters," the force added in a statement. Seven of the nine protesters have been arrested, but two remain on the runway.

The airport said inbound flights were being diverted and would be resuming operations "as soon as possible".