A man driving a stolen truck rammed into eight cars in the town of Limburg in western Germany on Monday evening, injuring 16 people, the German dpa news agency reported.
The heavy goods vehicle collided with the cars near traffic lights at around 5:20 p.m. local time (1520 GMT), thrusting them together. Police said that several people were trapped in their cars.
One person is "very seriously injured and in critical condition," a spokesman for the police force in the state of Hesse said.
The driver, who was also injured in the incident, has been arrested.
The background to the incident is not yet clear, and police are investigating whether the crash was a traffic accident or an attack, according to dpa.
Police said it was too soon to speculate about a motive.
"We currently do not have sufficient information about what was behind it," they said, according to the AFP news agency. "The investigation, including questioning witnesses and collecting evidence, is ongoing."
Authorities urged users of social media not to jump to conclusions on the motive.
"We are not ruling anything out," a spokesman for the state police force quoted by dpa said. "But we call on you: don't take part in speculation!" the regional police wrote in several tweets.
Germany has been on alert following several attacks in recent years claimed by the Islamic State (ISIS) jihadist group.
The worst such attack took place in December of 2016, when Tunisian terrorist Anis Amri killed 12 people and injured dozens more when he drove a truck into a Christmas market in Berlin.
In another attack, in July of that year, a 17-year-old Afghani with an axe attacked passengers on a train in Wurzburg before being shot dead by security forces.
In a second incident, an attacker set off a bomb in a restaurant in Ansbach, killing himself and wounding 12 others.