Protesters have blocked off five major bridges in central London as part of a so-called “rebellion day”.
Hundreds have gathered in central London to demand the government takes greater action on climate change.
Demonstrators have occupied Southwark, Blackfriars, Waterloo, Westminster and Lambeth bridges, causing “significant” traffic issues in the capital.
The mass protest follows a co-ordinated week of action around the UK by campaign group Extinction Rebellion.
At the start of the week, activists blockaded the UK’s energy department by chaining themselves together on the pavement.
Large groups of people holding banners began congregating on the five bridges from 10:00 GMT before blocking off the traffic.
The Met said the protests had caused “significant traffic disruption” although the bridges remained open to pedestrians.
Tiana Jacout, of Extinction Rebellion, said the bridge blockages were “not a step we take lightly” but “if things continue as is, we face an extinction greater than the one that killed the dinosaurs”.
“We have tried marching, and lobbying, and signing petitions. Nothing has brought about the change that is needed,” she said.
It is believed about 50 people have been arrested for taking part in action over the last week.