Environmental protesters have briefly blocked Waterloo Bridge in London and cut off access to other landmarks as they try to bring the city to a standstill.
The group Extinction Rebellion is trying to block five central London locations Monday to demand the British government declare a climate emergency.
The group expects thousands of protesters to converge on Marble Arch, Oxford Circus, Waterloo Bridge, Piccadilly Circus and Parliament Square.
Extinction Rebellion drew attention to its cause two weeks ago when members stripped to their underwear in the public gallery in Parliament during a Brexit debate.
Police have advised Londoners to leave extra time for their journeys because of possible delays caused by the protest.