Thousands of people have protested against the expansion of a coal strip mine in western Germany that would require clearing an ancient forest.
Police in the nearby city of Aachen said some 4,000 protesters joined Sunday's march towards Hambach Forest, which is home to centuries-old trees and hosts a protected species of bat.
Some demonstrators carried saplings they planned to plant between the woodland and an adjacent brown coal mine run by German utility company RWE.
Authorities have been trying for days to evict environmentalists who have constructed treehouses and chained themselves to tree trunks in the forest to stop the clearing, which entered its fourth day on Sunday.
Around 150 people have made a home in the forest as part of the protest, according to dpa news agency. Some have been living in treehouses without electricity and running water for as long as six years.
Environmentalists say gradual encroachment by the neighbouring Hambach mine has seen the forest shrink to about 10 percent of its original size.
A Twitter account set up in the name of the forest has shared images of riot police, cranes demolishing the makeshift "Oaktown" treehouse settlement and crowds of protesters
The activists have gained support from international environmental groups, such as Greenpeace, who said in a statement on Twitter on Sunday that the demonstrators are "not only defending a 12,000-year old forest, they're trying to protect the planet".
Evictions began on September 5 in order to prepare the forest for clearing.
On Saturday, 30 people were arrested as police ordered the demonstrators to abandon their camp in the largest confrontation since protests began.
Firefighters had to pump fresh air into a makeshift tunnel after at least five activists attempted to hide out there.
RWE wants to clear the forest to mine lignite, which it says is needed to guarantee fuel for the country's coal-powered energy plants.
In a statement, the energy company said the occupation of the forest "jeopardises supplies to nearby power plants and refining plants", adding that around 15 percent of electricity requirements for North Rhine-Westphalia - the state where the forest is located - are met by coal from the Hambach mine, which is the largest opencast mine in Germany.
Environmentalists are pinning their hopes on a government-appointed committee, set up to examine the future of Germany's coal industry, who could recommend halting large-scale chopping down of trees in Hambach Forest.
|Some of the 150 people living in makeshift shelters in the forest have been there since protests began in 2012 [Thilo Schmuelgen/Reuters]|