THE city of Graz in southern Austria has been left in a state of shock after a man drove his SUV into crowds in a busy city centre before stabbing bystanders with a knife - leaving three dead and 34 injured.

The area was sealed off as large numbers of ambulances and helicopters arrived at the scene to treat the victims, who were being helped by shocked witnesses.

Police, who have arrested the driver, say there are no indications the attack was an act of political terrorism.

Six of those who were injured are believed to be in a critical condition, while two people are said to be seriously injured but stable.

The spree appears to have started in a run-down district in the south-east corner of the city, where the driver is believed to have mown down at least three people.

He then headed east towards the central district, crashing into and stabbing a couple, who looked to be in their sixties, who were left lying on a grass verge bleeding and in shock.

The motorist then headed north to the main shopping avenue where he mounted a pavement and rammed into the large crowds of shoppers, as well as diners outside a fish restaurant where eight people were injured.

Terrified pedestrians then ran for their life as the car entered a nearby square, which was hosting an event related to the Austrian Formula 1 Grand Prix, travelling at between 60mph and 90mph.

Eye witnesses said some of those hit by the dark green off-road vehicle were launched on to the windscreen before being flipped over the car.

The driver, a 26-year-old Austrian, then drove a few hundred metres to a police station where he is understood to have handed himself in.

Shortly after the incident, the town centre swarmed with police, ambulances and helicopters, as well as thousands of bewildered shoppers, who were all encouraged to call home and let friends and family know they were safe.

One witness, a visibly-shocked shopkeeper in his 40s, said he saw three people injured outside a supermarket and two dead. "I'm shocked, I'm really shocked," he said as he walked away from the scene.

Art gallery worker Helmut Reinisch added: "I heard a little hissing sound as [the car] went past. Then I heard loud screams and went out and saw lying on the ground a child and a man and two bikes that looked as if they had been rolled over.

"I immediately called the rescue services, but the driver got out and attacked with a knife before anyone could arrest him."

Police say the unnamed suspect was living in the south of the city.

He is said to be a professional driver who is married with two children who he was legally barred from seeing them on May 28 because of domestic violence.

Josef Klamminger, the regional police commander, ruled out a political terrorist motive for the attack saying it was the act of a "lone wolf".

This was echoed by provincial governor Hermann Schuetzenhoefer, who described the motorist as a "deranged" lone assassin, adding: "There is no explanation, there is no excuse."

The rampage was apparently the result of psychotic episode which was not believed to have involved drugs or alcohol.

The city mayor, Siegfried Nagl, witnessed the early stage of the incident himself while out on his scooter.

Black flags were hung throughout the city and residents were invited to make the main square a "sea of candles" in memorial to the victims.

Last night, barriers were still in place preventing people from entering the square, but candles were being placed as close to the barriers as possible.

A memorial service for the victims was also held last night in a city centre church.