The Republic of Ireland was last night coming to terms with the deaths of five young Irish students and an Irish-American woman when a fourth floor apartment balcony in California gave way beneath their feet.
Seven other students were seriously injured in the accident, which happened in the university town of Berkeley at 1am local time as a 21st birthday party was in full swing.
All were rushed to hospitals where two are thought to have life-threatening injuries, while the others are all seriously hurt.
The names of the students who died when the balcony collapsed were released last night. They were: Niccolai Schuster (21) and Eoghan Culligan (21), both former pupils of St Mary's College in Rathmines, Dublin; Eimear Walsh (21); Lorcan Miller (21); Olivia Burke (21) and her cousin Ashley Donohoe (22) - an Irish-American living in the Bay area.
All the dead students were thought to be from the south Dublin area.
A Belfast film student was asleep in the same apartment building when he was woken by the sirens of emergency vehicles racing to the scene.
Conor Maguire (21), from Finaghy in south Belfast, said he was stunned at the tragedy.
He said: "I feel terrible talking about this because I'm alive and there are people dead. It's unbelievable."
He said he heard that between 12 and 14 people were on the balcony at the time.
"It seems like most of the students at the party were from Dublin and I know two of the girls involved were studying at University College Dublin. I think they have died.
"It's been incredible watching this on TV this morning because the accident happened in the same building. The whole experience has been very surreal."
A son of Ann Travers, whose sister was shot dead by the IRA in an attack on her father, Judge Tom Travers, was at the party but escaped injury.
The father of a young Trinity College psychology student who survived the 40ft fall from the Berkeley apartment says his daughter "just fell from the sky".
Niall Cogley said it is a "miracle" his daughter Clodagh (21) is alive following the balcony collapse. She is being treated in hospital for "a number of broken bones" he added.
Philip Grant, Irish Consul-General in San Francisco, said the first family members of the dead and injured would arrive in Berkeley today.
All the Irish victims were thought to be in the USA on J1 student visas.
Irish President Michael D 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.
Speaking in the Dail, Taoiseach Enda Kenny said: "It is with great sadness that I can confirm that a number of young Irish citizens have lost their lives, while a number of others have been seriously injured.
"It is truly terrible to have such a serious and sad incident take place at the beginning of a summer of adventure and opportunity."
There will be a minute's silence in the Dail today and flags will fly at half-mast at Leinster House and other government buildings in memory of those who lost their lives.
Deputy First Minister Martin McGuinness tweeted: "Shocking news of the death of several young Irish people in a tragic accident in California.
"My heart & sympathy goes out to their families,"
Student leader Laura Harmon called on all Irish students in the USA to contact their families at home.
In Berkeley, three separate investigations are now under way into why the fourth storey balcony in the 2007 apartment block collapsed.
The tragedy is the third such major US balcony collapse in 12 years.