A man drove a van into a group of people sitting outside a popular restaurant in the old city center of Muenster in western Germany on Saturday, killing at least two of them before shooting himself dead, police said.
The vehicle ploughed into people sitting at tables outside the Grosser Kiepenkerl restaurant, which is popular with tourists.
"A vehicle drove into the outside area of the restaurant ... three people were killed, 20 injured, and six of those seriously injured," a police spokesman said, adding: "The perpetrator killed himself in the vehicle."
It was not immediately clear whether the perpetrator was among the three killed, or whether his death took the number of dead to four. A police spokeswoman said separately that there were at least three people dead.
The identity of the perpetrator was not yet clear, the spokesman said. Investigators were looking at the possibility that other suspects fled the scene, though they had no evidence this was the case, he added.
"It is far too early to speak of an attack," he said.
The police spokeswoman said: "The danger is over."
The incident came one year to the day after a truck attack in Stockholm that killed five people, and also evoked memories of a December 2016 truck attack in Berlin that killed 12 people.
Anis Amri, a failed Tunisian asylum seeker with Islamist links, hijacked a truck on December 19, 2016, killed the driver and then ploughed it into a crowded marketplace, killing 11 more people and injuring dozens of others.
"I am shocked by the news from Muenster," said Andrea Nahles, parliamentary leader of the Social Democrats, junior partner in Chancellor Angela Merkel's ruling coalition.
"My thoughts are with the victims and their relatives," she added. "I hope that our authorities can quickly clarify the background to this incident and wish the local forces much strength for their work."