At least one person has died and several others injured after a vehicle drove into a crowd in western Berlin, police say.
A man believed to be the driver of the vehicle has been detained, they added.
It is unclear whether the incident was the result of an accident or whether the driver had intentionally driven into the crowd, Berlin police spokesman Martin Dams said.
The man had been driving a small Renault car, Germany’s Bild newspaper reported.
According to witnesses, he initially ran away and was stopped and handed over to police, it added.
Footage from the scene showed the silver car had crashed into the window display of a department store.
The fire service said around 30 people were injured in the incident.
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It took place on Rankestrasse, near the main shopping district’s Breitscheidplatz, the scene of the 2016 Christmas market attack in which 11 people were killed.
Actor John Barrowman, who was at the scene, spoke of “multiple fatalities”.
“We think we have witnessed a terrorist attack here in Berlin,” he tweeted from the German capital.
“We’re not sure – there’s a lot of people dead bodies all over the place.
“We’ve seen a car that came down the road and ended up in a storefront covering three city blocks. It’s pretty horrific.”
“It’s really pretty bad, guys,” he continued in video messages posted on social media.
“There are police behind us, there are other police cars coming. There’s helicopters coming in. This is bad. This is serious, because there’s multiple fatalities.
“There are hundreds of emergency services that are in the area, blocking city block after city block, off. The cordon keeps expanding.”
