President Michael D Higgins has expressed sadness at the deaths of six young Irish people in a balcony collapse in Berkeley, California.
Speaking from Italy, where he is on an official visit, President Higgins said: "I have heard with the greatest sadness of the terrible loss of life of young Irish people and the critical injury of others in Berkeley, California today.
"My heart goes out to the families and loved ones of all those involved.
"I have been informed of the consular assistance being provided to assist all of the families involved and I have asked to be kept informed as further details emerge."
Taoiseach Enda Kenny made a statement in the Dáil sympathising with the parents of the J1 students who lost their lives in Berkely, saying his heart breaks for the parents.
"It is truly terrible to have such a sad incident take place at the beginning of a summer of opportunity for young poeple on J1 visas.
He said there were 13 people on the balcony at the time of the incident.
Taoiseach expresses sadness at the deaths of five Irish citizens in Berkeley, California https://t.co/0VcauUkb5f
— RTÉ News (@rtenews) June 16, 2015
Meanwhile, Tánaiste Joan Burton said her "heart goes out to the families of the Irish students who died tragically in Berkeley early today.
"Hearing news like this about a loved one far away would be any parent's worst nightmare," she said.
Opposition politicians have also expressed their sympathy in the Dáil, with Fianna Fáil's Micheál Martin saying hearts and minds go out to the parents and their families.
University College Dublin president Andrew Deeks said we cannot comprehend the "desperate shock and grief" the families and friends of those killed and injured are experiencing.
He said the university has been in touch with colleagues in University of California Berkeley and they have offered to place their counselling services at the disposal of Irish students in the area.
He added: "Our students, like thousands of others across Ireland, head to the US each summer on J1 visas to enjoy the experience.
"It is heart-breaking to imagine that such a tragedy would strike these wonderful students when their lives are opening up to discover the world."
A book of condolence has been opened online.
UCD Students' Union president Marcus O'Halloran said he is deeply saddened by what happened in Berkeley. He said the union is available to students, even those abroad, and is offering a welfare and referral services to student advisers and counsellors.
Irish Ambassador to the US Anne Anderson said: "It is heart-breaking to think of these bright young lives cut short.
"All our thoughts are with the bereft families, and with those seriously injured and their loved ones.
"Our Consulate in San Francisco and our consular services in Dublin are providing every possible assistance."
Sinn Féin's Gerry Adams said their thoughts were with the families and friends of those who died, and those who were injured.
Independent TD Finian McGrath noted that many TDs had children that went to the US on J1 visas.
He said it was a "horrific" and "sad day" for the parents of those who died and he offered sympathy on behalf of the Technical Group.
Statement from @USAmbIreland on the tragic deaths of Irish students in California pic.twitter.com/wD2wJTsYhi
— U.S. Embassy Dublin (@USEmbassyDublin) June 16, 2015
US Ambassador to Ireland Kevin O’Malley said: "I would like to offer my heartfelt sympathy and condolence to the families, loved ones, and friends of the Irish students who lost their lives this morning in Berkeley California.
"All of us at the United States Embassy are greatly saddened by news of this tragic incident and are ready to do whatever we can to assist the Irish Department of Foreign Affairs at this difficult time. We will continue to co-ordinate as more details become available.
"Our thoughts and prayers are with the families, loved ones, and friends at this difficult time."
The Union of Students in Ireland said it is shocked and deeply saddened at the news.
USI President Laura Harmon said: "The thoughts and sympathies of the whole student movement in Ireland are today with the families and friends of those young people caught up in this terrible event. We are anxiously awaiting further information from the authorities."
Minister for Diaspora Affairs Jimmy Deenihan said "the loss of life in such tragic circumstances is an enormous blow to the families involved and to the country."
Catholic Primate of All Ireland Archbishop Eamon Martin said the "devastating news will be felt by Irish people everywhere, and particularly by those who have family and friends abroad."
Archbishop Martin said he is praying that "the eight injured students will fully recover from this terrible accident."
Dublin Lord Mayor Christy Burke has said a Book of Condolence will be opened at the Mansion House on Thursday and Friday.
In a statement, he said: "I am opening a Book of Condolence to allow the people of Dublin to express their sympathies to the families and friends of those who died in this terrible tragedy.
"I offer my personal sympathy to all who have suffered the loss of loved ones and, at this time, my thoughts and prayers are with all those who have been affected by this tragic event."
US Ambassador to Ireland Kevin O'Malley described getting the news of the tragedy in Berkeley as "just unbelievable."
Mr O'Malley described the students as "bright, young and talented" and said that many of them were known to the Embassy as they had attended J1 send-off parties.
He described it as "personal and very tragic" and as "a very sad day for all of us."
The President of the Methodist Church in Ireland has expressed his shock and sadness at the deaths.
Rev Brian Anderson said: "As a father of similar aged young adults I can imagine how I would have felt being told such tragic news and so I would like on my own behalf and that of the Methodist Church in Ireland to offer sincere sympathy and prayers to those who have lost loved one and best wishes to those whose young people are critically ill.
"I am also mindful of many parents who are anxiously waiting news of their own young people."
Desperately sad news from the US, of those Irish students killed or injured. We've all done that J1 trip; we will all share the loss.
— Dara Ó Briain (@daraobriain) June 16, 2015
Card left at scene of #balconycollapse #Berkeley pic.twitter.com/bKGJR5krLb
— Jessica Guynn (@jguynn) June 16, 2015