A doctor from Saudi Arabia deliberately drove his vehicle through a Christmas market in Magdeburg, in eastern Germany.
Some media reports say five people were killed and up to 80 injured after being hit by the black BMW.
The regional interior minister described it as a terror attack.
The driver has been arrested. Police said some sort of explosive device as found inside the vehicle.
A disturbing video shows a speeding car plowing through dozens of pedestrain at the busy Christmas market.
Reuters is reporting a spokesperson for the city of Magdeburg says all hospitals in the area are preparing for a "mass casualty event."
BILD reported the attacker a 50-year-old Saudi Arabian national.
Alice Weidel, leader of the far-right Alternative for Germany (AfD) party, described the images from Magdeburg as "devastating" and said her thoughts were with "those left behind and injured."
"When will this madness end?"
In an interview with Bild newspaper, 32-year-old Nadine says she had her boyfriend Marco in her arms when the car came hurtling towards them.
"He was hit and pulled away from my side. It was terrible," the 32-year-old tells the German newspaper.
"The uncertainty is unbearable", she adds, as she doesn't yet know which hospital her partner has gone to.
Magdeburg, which is west of Berlin, is the state capital of Saxony-Anhalt and has about 240,000 people.
German Chancellor Olaf Scholz said the incident "raises the worst fears."
"My thoughts are with the victims and their loved ones. We stand by their side and by the side of all Magdeburg residents. My thanks to all the emergency services in these difficult hours."
Tensions have been running high in Germany after a mass influx of Middle Eastern migrants.
...more to come
