At least three people are dead and dozens injured after a man drove his car into crowds in a square in Austria's second largest city of Graz.
The driver has been arrested, though police say there were no indications the attack was motivated by terrorism.
Part of the city was sealed off, with large numbers of ambulances and helicopters sent to the scene.
The square in Graz was hosting an event related to the Austrian Formula 1 Grand Prix, which is being held nearby.
The regional governor confirmed that three people had died and 34 were injured, some seriously.
Hermann Schuetzenhoefer told reporters that the suspect was a 26-year-old man who was "mentally unbalanced".
"There is no explanation, there is no excuse," he added. Austrian Chancellor Werner Faymann also said he was deeply shocked by the incident.
Sixty ambulances and four helicopters were sent to the scene.
Eyewitness Helmut Reinisch told the BBC he saw bodies lying on the ground "covered in blood," including a young boy.
He added that the car was travelling at least 100 km/h: "It was really horrible, everybody was shocked."
The city's mayor, Siegfried Nagl, witnessed the incident.
"The driver deliberately drove into pedestrians. I myself saw a woman being run over," he told Kleine Zeitung newspaper.
Another witness described a lucky escape.
"I was having cappuccino on the main square when people started screaming and then there was the loud noise coming from a car engine. I leapt to safety in a nearby arcade."
The Austrian Grand Prix takes place this weekend in Spielberg, and it is thought that many of the city's emergency services had been deployed there.
The mayor has cancelled all city events in Graz and ordered black flags of mourning to be raised above municipal buildings, AP reports.
There are unconfirmed reports that after crashing the man left the vehicle and attacked people with a knife.