Climate campaigner Greta Thunberg was detained alongside other activists on Tuesday during protests against the demolition of a village in Germany to make way for a coal mine expansion, but she was released after an identity check, according to police.

"There is no reason to hold them for days. It might take hours or they will go immediately," a spokesperson for regional police in Aachen said, speaking about the whole group of demonstrators.

Thunberg was held while protesting at the opencast coal mine of Garzweiler 2, about nine kilometres from Luetzerath, where she sat with a group of protesters near the edge of the mine.

The clearing of the village in the western state of North Rhine-Westphalia was agreed to between energy company RWE and the government in a deal that allowed the energy giant to demolish Lutzerath in exchange for its faster exit from coal and saving five villages originally slated for destruction.

Activists have said Germany should not be mining any more lignite coal and should instead focus on expanding renewable energy.

Riot police backed by bulldozers removed activists from buildings in the village with only a few left in trees and an underground tunnel by last weekend, but protesters, including Thunberg, remained at the site staging a sit-in into Tuesday.

Thunberg was seen sitting alone in a large police bus after having been detained, a witness said.

She had been "part of a group of activists who rushed toward the ledge," a spokesperson for Aachen police told Reuters, adding that one activist had jumped into the mine.

"However, she was then stopped and carried by us with this group out of the immediate danger area."

She was carried away by three police officers and then escorted toward police vans.

The Swedish climate activist addressed the roughly 6,000 protesters who marched toward Lutzerath on Saturday, calling the expansion of the mine a "betrayal of present and future generations."

"Germany is one of the biggest polluters in the world and needs to be held accountable," she said.