Police broke up a two-day protest outside the Swiss parliament overnight, carrying away demonstrators who had camped out to demand more action against climate change, the ATS news agency reported Wednesday.

They swarmed the square in the middle of the night, forcibly removing protesters chanting "Protecting the climate is not a crime", ATS reported.

"Tonight the police were made a tool of political ignorance," the activists lamented on the Collective Climate Justice Facebook page. "Institutional politics did what it has been doing for decades: once again it treats the climate movement rather than the climate crisis as the problem!"

Several hundred protesters had set up camp on the square outside the parliament building in central Bern in the wee hours of Monday under the banner "Rise Up for Change", aiming to pressure MPs as they are holding their autumn session.

Protests on the square while parliament is in session have been prohibited by law since 1925, and parliamentarians had asked to have the activists removed. The municipality of Bern repeatedly asked the protesters to move to a nearby location, but to no avail, and they also ignored a final ultimatum issued by the police late Tuesday to clear the square.

In the end, police cordoned off the square at around 2:00 am (0000 GMT), and around 30 of the protesters who agreed to filter out on their own were permitted to leave after providing their personal details.

By 3:30 am, police moved in to evacuate the sit-in, carrying away protesters who refused to walk out on their own, and cutting the chains some had used to tie themselves down. Police spokesman Christoph Gnagi told reporters that the evacuation had been peaceful, with no injuries.

The protesters criticised the decision to clear the square. "An urgent and legitimate protest has been blocked," Frida Kohlmann, of the Climate Justice collective, told ATS. "The powerful of this world do not want to hear our message."