Protesters on Thursday fought running battles with police, torched vehicles and looted shops in Dublin, after three young children were injured in a knife attack outside a school.

Near O'Connell Bridge, over the River Liffey, flames rose from a torched car and bus, while crowds broke into stores and looted one of the city's main shopping streets.

"What we saw last night was an extraordinary outbreak of violence," Garda Commissioner Drew Harris said Friday. "These are scenes that we have not seen in decades."

The unrest — the worst in Dublin in years — came after a five-year-old girl sustained serious injuries in a suspected stabbing in Parnell Square East, north central Dublin.

Two other children and two adults — a woman and the suspected perpetrator of the attack — were taken to hospital after the incident around 1:30 p.m.

Rumors on social media about the nationality of the assailant, who police only described as a man in his fifties, helped fuel unrest following the attack.

Police chief Drew Harris blamed a "complete lunatic faction driven by far-right ideology" and warned against "misinformation."

Some protesters carried signs reading "Irish Lives Matter" and waved Irish flags through a neighborhood home to a large immigrant community.

Witness Siobhan Kearney said the scene was "absolutely bedlam" as she initially watched events unfold from the other side of the street.

"Without thinking, I just took across the road to help out," she told Irish national broadcaster RTE.

"We got another young man, disarmed (the attacker) with the knife. Another man took the knife and put it away for the (police) to find it."

Kearney added a group of people restrained the suspect on the ground as some of those injured were taken back inside the school.

"Gardai (Ireland's national police) have detained a suspect and are following a definite line of inquiry," Prime Minister Leo Varadkar said.

By late evening, Police Chief Superintendent Patrick McMenamin said calm had been restored and no serious injuries were reported.