Police in the German city of Magdeburg have so far confirmed the deaths of four people in a car ramming attack on a Christmas market, the Bild newspaper reports.
According to the law enforcement agencies, a total of 205 people suffered injuries, with 41 being in critical condition.
Reiner Haseloff, the premier of the state of Saxony-Anhalt, told reporters at the scene that the suspect - who has been arrested - was a 50-year-old Saudi citizen who arrived in Germany in 2006 and had worked as a doctor, BBC reports.
He said a preliminary investigation suggested the alleged attack was acting as a lone wolf and that he could not rule out further deaths due to the number of injured.
The suspected attacker's motive is unclear, and he has no known links to Islamist extremism - social media and posts online appear to suggest he'd been critical of Islam.
Footage from the scene shows numerous emergency services vehicles attending while people lay on the ground.
Further footage then emerged of armed police confronting and arresting a man who can be seen lying on the ground by a stationary vehicle.
Unverified video on social media purports to show a car ploughing into the crowd at the market.
City officials said around 100 police, medics and firefighters, as well as 50 rescue service personnel rushed to the scene.
German Chancellor Olaf Scholz said: "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."
Scholz will visit the city on Saturday, Haseloff said, and there will be a memorial service for the two victims at the Magdeburg Cathedral.
In an interview with German paper Bild, Nadine, described being at the Christmas market with her boyfriend, Marco, when the car came speeding towards them.
"He was hit and pulled away from my side," the 32-year-old told the paper. "It was terrible."
Meanwhile, Lars Frohmüller, a reporter for German public broadcaster MDR, told BBC Radio 4's World Tonight he saw "blood on the floor" as well as "many doctors trying to keep people warm and help them with their injuries".
