Activists in northern Germany have been fighting running battles with police, trying to halt a train carrying nuclear waste from France.
Officers used batons, pepper spray, tear gas and water cannon to disperse at least 1,000 protesters who were trying to sabotage railway tracks.
The protesters hurled fireworks and set a police car on fire near Dannenberg.
Earlier, the train was halted after activists lowered themselves on ropes from a bridge over the tracks.
Sunday's clashes took place near Dannenberg - the final destination for the train before the waste is loaded onto lorries and taken to a storage facility.
A police spokesman was quoted by the AFP news agency as saying that "there were arrests and people injured but I am not able to say how many".
The spokesman added that some of the protesters appeared to be "members of the anarchist scene, who threw flares and fired tear gas at police".
About a dozen protesters were injured, demonstrators were quoted as saying by local media reports.
One of the activists was quoted by the AFP as saying that the woods around the train tracks were "completely clouded with tear gas".
Sunday's clashes followed peaceful protests against the train on Saturday by tens of thousands of people.
The train, made up of 14 wagons containing 123 tonnes of reprocessed nuclear waste in glass and steel containers, is heading to a storage site in Gorleben, northern Germany.
Activists maintain that neither the waste containers nor the site are safe.
The BBC's Berlin correspondent Stephen Evans says that the plan is to transfer the waste to lorries for the final part of the journey but the police and protesters are now trying to outmanoeuvre each other in the countryside along the route.
Chancellor Angela Merkel's decision to extend the lifespan of Germany's 17 nuclear power plants despite strong public opposition has highlighted the issue of the waste trains.