A 14-year-old boy died, and five other people were injured in a knife attack in southern Austria on Saturday, police said, adding they have arrested a 23-year-old Syrian asylum seeker.

"A man randomly attacked passersby with a knife," police spokesman Rainer Dionisio told AFP of the incident in the city of Villach.

"One victim, a 14-year-old boy, died," he added.

Two other men suffered serious injuries, while another two men were lightly injured, Dionisio added.

The incident happened on Saturday just before 4pm local time (2300 HKT) in the centre of the city, the capital of Carinthia Province.

A food delivery rider saw the attack and rammed his vehicle into the attacker, who was lightly injured and was arrested "right after the attack," according to Dionisio.

The man under arrest is a Syrian asylum seeker with a valid residence permit and without a criminal record, according to preliminary information, he added.

The youngest victim was the 14-year-old, while the oldest is 32 years old, he said. (AFP)