Five people including three children have been hospitalised after an incident in the city centre.
One girl aged 5 has sustained serious injuries and is currently receiving emergency medical treatment in CHI Temple Street.
A woman in her 30s is being treated for serious injuries at the Mater Hospital.
Two other children and a man are said to have less serious injuries.
The stabbing happened at Parnell Square at around 2pm.
Gardaí say they're not looking for anyone in connection to the incident.
The Education Minister says the National Educational Psychological Service is providing support to the school community.
"Person Of Interest"
In a statement, gardai say: "An Garda Síochána continue to investigate all the circumstances of a serious assault which occurred on Parnell Square East shortly after 1:30pm this afternoon Thursday, 23rd November 2023.
"Preliminary indications are that a male attacked a number of people on Parnell Square East.
"Five (5) casualties have been taken to hospitals in the Dublin Region.
"These casualties include three (3) young children, an adult female and an adult male.
"One girl aged 5 has sustained serious injuries and is currently receiving emergency medical treatment in CHI Temple Street.
"A boy aged 5 and a girl aged 6 years, who received less serious injuries were brought to CHI Crumlin for treatment. The boy has since been discharged from CHI Crumlin.
"An Garda Síochána is providing support to the children's parents.
"The adult female in her 30s is being treated for serious injuries at the Mater Hospital.
"An adult male in his 50s is also being treated for serious injuries at a Hospital in the Dublin Region.
"The scene remains sealed off at this time and a technical examination of the scene is ongoing.
"An incident room has been established at Mountjoy Garda Station and a Senior Investigating Officer has been appointed.
"An Garda Síochána is following a definite line of inquiry. The male in his 50s is a person of interest in this investigation. An Garda Síochána is not looking for any other person at this time.
"An Garda Síochána continues to have an open mind at this early stage of the investigation.
"An Garda Síochána is appealing to any person with any information on this attack to contact investigating Gardaí. Investigating Gardaí are also appealing to any person who may have mobile phone footage of the attack or the immediate aftermath to make this footage available to An Garda Síochána.
"Anyone with information is asked to contact Mountjoy Garda Station 01 6668600 the Garda Confidential Line 1800 666 111 or any Garda Station."
"Deep Shock"
The Justice Minister has expressed her "deep shock" at an attack on three "innocent" children and a woman in Dublin.
Helen McEntee says her thoughts are with those injured, especially the children and their families.
The Minister has been briefed on the situation by senior Gardaí.
She says he has "no doubt" the person responsible will be brought to justice.
Taoiseach Leo Vardakar says: "We are all shocked by the incident which has taken place in Parnell Square. A number of people have been injured, some of them children. Our thoughts and our prayers go out to them and their families.
" The facts in this matter are still emerging. The emergency services responded very quickly and were on site within minutes. I thank them for that.
"Gardaí have detained a suspect and are following a definite line of inquiry."
