A German man plowed his car into a carnival parade in the western town of Volkmarsen on Monday, injuring 30 people including children, police said, adding it was too early to say what his motive was.
German prosecutors and police said the suspect, a 29-year-old German citizen, was being treated for injuries sustained in the incident and they were looking into all possibilities.
The police believed the driver had acted deliberately, but that they could not question him due to his injuries.
The incident comes less than a week after a man shot dead nine people before killing his mother and himself, in one of the worst racist attacks in Germany since World War Two.
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.