Several thousand people blocked five iconic London bridges today (Nov. 17) to protest government inaction on climate change, as part of a month-long campaign of mass civil disobedience planned by a group known as Extinction Rebellion.

For the past few weeks, Extinction Rebellion has encouraged people to commit non-violent acts of civil disobedience ranging from gluing themselves to government buildings to planting trees in parliament square. Now, thousands of Britons have answered calls to block major roads in the British capital as part of the group’s “Rebellion Day.” The day-long protests are expected to culminate in an interfaith ceremony outside Westminster Abbey.

According to representatives of the group, more than 6,000 protesters blocked Blackfriars, Waterloo, Southwark, Westminster, and Lambeth Bridges from 10 am onwards on Saturday. City officials arrested at least 50 people under the Highway Acts of 1980, which states that “If a person, without lawful authority or excuse, in any way willfully obstructs the free passage along a highway he is guilty of an offense” and liable to pay a fine of up to £1,000.

Smaller protests also took place in other major urban centers across the United Kingdom, including cities like Cork, Ireland:

Extinction Rebellion bills itself as a group of “concerned citizens” focused on the environment. It gained national prominence in October, when close to 100 high-profile figures from across the United Kingdom published an open letter of support in The Guardian, stating that it is “not only our right, but our moral duty to bypass the government’s inaction and flagrant dereliction of duty, and to rebel to defend life itself.” Now, Extinction Rebellion is planning large-scale events in other countries, including the United States.

The Rebellion Day protests come at a time of renewed global anxiety over the pace and impact of climate change. A recent United Nations report written by 91 leading climate scientists warns that the world only has about a dozen years left to prevent a global ecological disaster. As Extinction Rebellion organizers have stated, this reality calls for urgent international action “in accordance with our conscience and as a clear duty to our children; our communities; this nation; and the planet.”