Dozens of people were injured after a driver rammed into a crowd in the German town of Volkmarsen, the authorities said.
The 29-year-old German citizen is reported to have intentionally rammed into the people at a carnival procession.
Several people including at least ten children were injured in the incident. Some of the victims were in critical condition.
The suspect was detained after being treated for his injuries. The motive of the attack was not immediately established.
Although the police said there was no indication of a threat anywhere else in the country, all carnival parades across the state were cancelled as a precaution.