Black Lives Matter protesters chained themselves together on the runway of London's City Airport on Tuesday, forcing all flights in and out of the business travel hub to be diverted for six hours.

Police were called at 5:40 am local time (0440 GMT) after protesters "erected a tripod and... locked themselves together," according to a statement from London police.

"Officers negotiated with the protestors and specialist officers arrived to 'unlock' the protestors," the statement said.

The process of removing the protesters began at 9:30 am, but it was not until around 11:30 am that the runway was finally cleared, blocking all flights for six hours.

Police arrested nine people were arrested on suspicion of aggravated trespass, being unlawfully airside and breaching London City Airport bylaws.

Tweeting that the runway had reopened. London City Airport apologised for the disruption and advised travellers to check with their airline for flight information.

The Twitter page of Black Lives Matter UK claimed responsibility for the protest, saying it was to highlight the "UK's environmental impact on black people".

"7/10 of the countries most affected by climate change are in sub-Saharan Africa," said another tweet.

Pictures from the airport showed the protesters lying down on the tarmac beneath a wooden tripod, next to a sign reading: "Climate Crisis is a Racist Crisis."

All flights due to land at the airport were diverted to Southend and Gatwick airports, near London.

London City Airport is located in the former docks area east of the city centre, close to Canary Wharf, one of the twin centres of London's finance industry.

The airport offers short-haul flights to locations in Britain and mainland Europe, and served over four million passengers last year, many of them travelling for business.

Its sole runway is surrounded by water, but it was reported that the protesters were able to either swim or use a dinghy to cross the wharf, raising questions about security.

Activists from Britain's Black Lives Matter movement blocked the main road into London Heathrow, Europe's busiest airport, last month as part of a nationwide day of protests against racism.