The demonstrators say the government's commitment to abandon fossil fuels by 2038 is not serious enough.
Hundreds of anti-coal protesters entered a mine in western Germany on Saturday to protest the continued extraction and use of fossil fuels.
Environmentalists object to the German government's decision to allow the mining and burning of coal in the country until 2038, a deadline the activists say is too late to effectively tackle climate change.
Activists are also protesting the planned destruction of several villages to make way for the expansion of the Garzweiler strip mine, west of Cologne.
Police and utility company RWE said some protesters broke into the mine and coal storage facilities early Saturday.
The Garzweiler mine and nearby power plants have been a focus of protests for several years. Environmentalists say they are among the biggest sources of harmful pollution and greenhouse gas emissions in Europe.