One person has died and several are injured after a car drove into a crowd of people in the German city of Mannheim a police spokesperson says, adding that one suspect had been arrested.
The official said it was unclear whether any other suspects were involved.
The police is appealing to the public in the western German city to stay at home.
The incident occurred as crowds gathered in cities across regions including Germany's Rhineland for parades to mark the Carnival season.
A black SUV drove at high speed into people, travelling from the centrally located Paradeplatz square towards the city's landmark water tower, the Mannheim24 news website reported.
A reporter from the DPA news agency at the scene witnessed a person being covered by a sheet among debris.
The police said the incident occurred at the Paradeplatz square in the city centre.
The police operation followed a "dangerous" incident, a police spokesperson told the broadcaster NTV.
Security has been a key concern in Germany following a string of violent attacks in recent weeks, including deadly car rammings in Magdeburg in December and in Munich last month as well as a stabbing in Mannheim in May 2024.
Police were on high alert for this year's carnival parades after social media accounts connected to the Islamic State militant group called for attacks on the events in Cologne and Nuremberg.
with DPA