Extinction Rebellion has continued to protest in central London despite a police order to leave Trafalgar Square.
Late on Monday police told protesters they faced arrest if they continued to demonstrate in central London.
Among those arrested was Green Party MEP Ellie Chowns, who said she was arrested on Monday night for "standing in solidarity" with protesters at Trafalgar Square.
Early Tuesday the group's co-founder Gail Bradbrook climbed the entrance to the Department for Transport in Westminster.
Ms Bradbrook smashed a window at the front of the Department for Transport building
Extinction Rebellion has caused disruption for more than a week as part of global protests to demand government action on climate change.
More than 1,400 people were arrested during the first eight days of protests, and those camped in Trafalgar Square were told they must have vacated by 9pm Monday.
By midnight only around 50 protesters remained and much of the activists’ infrastructure had been removed.
Extinction Rebellion said police were breaking the law by clearing a “peaceful protest”.
“This is an emergency, and an outrage. The police must respect the law. This is a democracy,” it said.
Met Police Deputy Assistant Commissioner Laurence Taylor said activists had caused “ongoing serious disruption to the community”.
“Officers have begun the process of clearing Trafalgar Square and getting things back to normal,” he said.
“The policing operation continues, and we will continue to take action against anyone engaged in unlawful protests at locations targeted by Extinction Rebellion.”
Activist Pam Williams, 71, glued herself to the spot where her tent stood and said she would not move.
“I'm refusing to leave and I've glued myself to the ground. My husband has taken away the tent, the police haven't got it. I shall stay here until I'm arrested,” she said.
Police are expecting the city to fill again on Saturday for an unrelated anti-Brexit protest.