A driver plowed his car into a carnival parade in the western German town of Volkmarsen on Monday injuring 30 people, including children, some of them seriously, police said on Monday.
Regional broadcaster Hessenschau said police believed the driver, identified as a 29-year-old German citizen, had acted deliberately, but that nothing was immediately known about his motive.
German news website HNA cited witnesses as saying the man appeared to have targeted children and had driven "at full throttle" into the crowd, which had gathered for the traditional procession ahead of the Christian season of Lent.
Asked how many were injured, a police spokesman in the regional center of Kassel said: "I would say about 30."
Police said on Twitter that some people were seriously injured, including children. Bild newspaper said a third of the injuries were serious and some were life-threatening.
Police assumed it was an attack but there were no indications that it was politically motivated, Bild said.
Police called off all carnival parades in the German state of Hesse, where Volkmarsen is located, as a precautionary measure, but said they were not aware of any danger elsewhere in Germany.
The incident comes less than a week after a man gunned down 11 people in the town of Hanau east of Frankfurt am Main, including himself, in one of the worst racist attacks in Germany since World War Two.
Carnival is hugely popular in parts of western Germany, especially in Rhineland cities such as Cologne and Duesseldorf, where festivities peak on "Rose Monday" with tens of thousands attending street parades featuring comical or satirical floats.
Police cars and ambulances rushed to the scene in Volkmarsen, a small town in northern Hesse, 260 miles (420 km) west of Berlin.
"We are on the ground with a big deployment. An investigation is underway," north Hesse police said on Twitter after the incident, which they said occurred at about 2:45 pm (1345 GMT).
Amateur pictures published online showed police officers standing next to a silver Mercedes-Benz car that appeared to have been involved.
German media said the driver deliberately broke through plastic barriers set up by police around the parade area, where 1,500 people were expected to gather.
The car had continued driving through the crowd for about 30 meters (33 yards) before coming to a halt, a witness told Hessenschau. Police were unable to question the driver, for the time being, Welt newspaper said, without elaborating.
In 2016, a Tunisian man with Islamist militant ties plowed a truck into a Christmas market in Berlin, killing 12 people. He was later shot dead by Italian police after he fled Germany.