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 shortly after 1.30pm.

Police chief Drew Harris blamed the unrest on a “complete lunatic faction driven by far-right ideology”.

He warned against “misinformation” as rumours spread on social media about the suspected attacker’s nationality.

One protester said: “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.

But 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”.

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 told 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 has since been discharged, he added.

The woman was being treated for serious injuries in hospital, while the man, said to be aged 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.

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 have detained a suspect and are following a definite line of inquiry.”

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 social media platform X, formerly known as Twitter.

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

“There is shock throughout the community. I have just spoken to the principal of Gaelscoil Cholaiste Mhuire and relayed my support to the school community,” she said in a statement.

“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 added, praising the police for their swift response.