Two people were killed and two others were seriously injured when a car drove into a central pedestrian zone of the eastern German city of Leipzig, Mayor Burkhard Jung told journalists at the scene.
Police arrested the driver, identifying him as a 33-year-old man with German citizenship. They said there was no further danger.
The prime minister of the state of Saxony, Michael Kretschmer, said that the suspect had possible mental health issues.
The police said they were conducting a large operation in the area and would be providing further updates.
A city press release called it a "mass casualty event".
The police could not provide details on injuries, but local media reported up to 20 people were injured.
A damaged Volkswagen SUV with a person on top of the vehicle was seen speeding through a pedestrian zone, local broadcaster Radio Leipzig reported.
Like other European countries, Germany has witnessed a spate of car-ramming and stabbing incidents in recent years, some of which involved religious or political motivations and some carried out by people with mental health issues.
Last year, two people were killed in the western city of Mannheim, when a 40-year-old man drove a car into a group of pedestrians, only weeks after a similar attack on a trade union demonstration in Munich, killing two and injuring more than 40, many children among them.
In December 2024, several people were killed in a car-ramming attack on a Christmas market in the eastern city of Magdeburg.
That incident came months after a stabbing attack at a festival in the western city of Solingen.
