At least two people were killed and 25 injured on Monday after a car ploughed into a crowd in the western German city of Mannheim.
German police said the driver had been arrested and it was not yet clear if there were other suspects.
Police urged the public to stay away from the city center.
Local authorities said, according to preliminary information, that the driver who hit the pedestrians was a German in his 40s.
Reuters news agency quoted a witness as saying that people were seen lying on the ground at the scene of the accident and that at least two were being revived.
The German newspaper Bild, citing security sources, reported that two people were killed and 25 injured.
It was not yet clear whether the driver had acted intentionally or whether there was any connection to the carnival celebrations in Germany.
