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, dressed in coloured overalls and braving wind and rain, are also protesting over the planned destruction of several villages to make way for the expansion of the Garzweiler strip mine, west of Cologne.
An Associated Press reporter witnessed some protesters break through police lines early on Saturday before being detained by officers.
Utility company RWE said some protesters also entered coal storage facilities.
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.
In her weekly video message, German chancellor Angela Merkel called for sustainable development, to help confront the threat of global warming.
Mrs Merkel cited Germany’s increase in renewable energy production as an example of the measures her country has taken. She did not mention coal mines.
