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.

Police in riot gear stood guard on the streets in the Irish capital as crowds taunted them with chants and set off fireworks.

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.

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 pm (1330 GMT).

Rumours 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 neighbourhood home to a large immigrant community.

One protester told AFP that "Irish people are being attacked by these scum."

Ireland has been facing a chronic housing crisis, with the government estimating that there is a deficit of hundreds of thousands of homes for the general population.

Widespread dissatisfaction has fed into a backlash against asylum seekers and refugees, and far-right figures have promoted anti-immigration sentiment at rallies and on social media with claims that "Ireland is full".

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

"It was gratuitous thuggery," he said.

- Backlash -

Justice Minister Helen McEntee said the scenes in the city centre, including attacks on police, "cannot and will not be tolerated" and promised to take action.

"A thuggish and manipulative element must not be allowed to use an appalling tragedy to wreak havoc," she said, calling for calm.

Thursday's incident, which police said was not thought to be terror-related, involved a man armed with a knife stabbing victims outside the school, according to media and eyewitnesses.

Witnesses described how a man had been disarmed, and Prime Minister Leo Varadkar said a suspect had been arrested.

Superintendent Liam Geraghty later told media that "a young girl aged five years has sustained serious injuries" and was receiving emergency medical treatment.

A five-year-old boy and a six-year-old girl sustained less serious wounds and the boy had since been discharged, he added.

The woman was being treated for serious injuries in hospital, while the man, said to be in his 50s, was a "person of interest" for police, revealed Geraghty.

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.

- 'Horrified' -

Varadkar said he was shocked by the incident.

"The emergency services responded very quickly and were on site within minutes. I thank them for that," he said in a statement.

"Gardai (Ireland's national police) have detained a suspect and are following a definite line of inquiry."

EU chief Ursula von der Leyen said she was "shocked" by the "brutal attack".

Local lawmaker Aodhan O Riordain of the Irish Labour Party said the incident was "disturbing".

"Hope injuries are not serious but it will (be) extremely traumatising regardless for all involved," he wrote on X, formerly Twitter.

Mary Lou McDonald, leader of the Sinn Fein opposition party, said she was "horrified" by what had happened.

"I want to send my solidarity to the families of those attacked. As a parent, I can only imagine what they are going through right now," she said.