STOCKHOLM (REUTERS) - Swedish police said they were investigating possible terror motives for a knife attack on Wednesday (March 3) in which at least eight people were injured, and that the assailant has been arrested after being shot and wounded.

Some of the victims were in serious condition and the suspect, a man in his 20s, was hospitalised after his arrest, a police spokeswoman told a news conference.

The man was previously known to police for minor crimes, she said.

All eight victims were hospitalised and three had life-threatening injuries, the Jonkoping regional council said on its website.

Police said the suspect attacked at least five different locations in Vetlanda.

"We have started a preliminary investigation of attempted murder but there are details in the investigation that make us investigate possible terror motives," regional head of police Malena Grann told a news conference.

Police were alerted to the attack in Vetlanda, a town of around 13,000 people, around 3pm and initially said it did not appear to be an act of terrorism.

"We heard a scream from the street. Then we saw a man enter the store, shouting that he had been stabbed," Asa Karlqvist, owner of a florist shop, told local newspaper Vetlanda-Posten.

"Blood was pouring from his shoulder, so we got towels and applied pressure on the wound," she said.

The situation was under control and there were no indications that anyone else was involved in the attack in the town of Vetlanda, 340km south of the capital Stockholm, police told journalists.

Prime Minister Stefan Lofven condemned the incident.

"We confront such heinous acts with the combined force of our society," he said in a statement, adding he was in constant contact with both the police and the security service.

In April 2017, a radical Islamist drove a truck into crowds of shoppers on a busy street in central Stockholm, killing five people before crashing into a department store. He was arrested and later sentenced to life in prison.