A stabbing that left a teenager dead and five others injured in southern Austria was an "Islamist attack", Austria's Interior Minister Gerhard Karner said on Sunday.

"It is an Islamist attack with IS connections," Karner told reporters in the southern city of Villach where Saturday's attack took place, referring to the Islamic State jihadist group.

He added the suspect -- a 23-year-old Syrian asylum seeker -- was radicalised online "in a short space of time".

In the attack in the centre of the city, a man went after passers-by with a folding knife, police said. 

The Syrian was arrested just after the attack, which a fellow Syrian food deliverer stopped by ramming a car into the attacker.

A 14-year-old boy died, while five other men were hurt, including two seriously. Among the wounded are two other teens, both aged 15, police said.

The suspect is an asylum seeker with a valid residence permit and no criminal record, according to police.