text: It happened at a 21st birthday party in the apartment in Berkeley, California.
  Five of the victims were from Ireland, and some of them were students at University College Dublin (UCD).
  UCD President Andrew Deeks expressed condolences to their families saying "we are heartbroken at their suffering and loss".
  Those who were killed have been named as:
  Several others have been injured, some of them very seriously.
  Ms Donohoe, who had dual US-Irish citizenship, lived in California while the other five who died all had home addresses in Ireland.
  Mr Culligan and Mr Schuster were both past-pupils of St Mary's College in Rathmines, Dublin.
  The majority of the victims were in the US on work visas, on the J1 USA summer work and travel programme.
  The families of some of the students who died have arrived in the United States from Ireland.
  In a statement, the UCD president said: "It is with deepest sadness that I speak of the tragic accident involving UCD students and their friends in San Francisco.
  "On behalf of the entire university community, I wish to extend our condolences to the families and friends of those who died and to those who were injured.
  "We cannot comprehend the desperate shock and grief they are feeling and we are heartbroken at their suffering and loss."
  UCD is opening an online Book of Condolence on its website and is offering its counselling and student support services to the bereaved in the US and Dublin.
  "Our students, like thousands of others across Ireland, head to the US each summer on J1 visas to enjoy the experience," Mr Deeks said.
  "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."
  In a statement on Tuesday night, St Mary's College paid tribute to its past pupils.
  "The thoughts and prayers of everybody in the St Mary's community are with the families of Niccolai and Eoghan, as well as the other Irish youngsters named by the US authorities this evening," the school statement said.
  "We also pray particularly for those injured, and their families."
  Ireland's Consul General in San Francisco Philip Grant said it had been a very traumatic time for everyone involved.
  "To have this happen at the start of this season is something that has left us all frozen in shock and disbelief," he said.
  "It touches every single family in Ireland."
  Mr Grant will lay a wreath at a ceremony near the site of the balcony collapse later.
  Fr Aidan McAleenan from St Columba's Church in Oakland near Berkeley, and who is originally from Banbridge, County Down, spent several hours with the injured and their friends.
  "It was very emotional driving out and getting to the hospital and then having to tell some of them that another friend had died," he told the BBC.
  "It was really hard to know what to say or what to do. We prayed with them.  Other people from the Irish community arrived. They are really devastated. That sense you have when you are totally shocked."
  Fr McAleenan and members of the Irish Pastoral Centre will be working closely with the families of the victims, and there will be a special Mass on Thursday.
  The national flag with be flown at half-mast at Irish Government Buildings as a mark of respect for those who died.
  A Book of Condolence will be opened at the Mansion House in Dublin later.
target: An Irish university has expressed "heartbreak" at the deaths of six young people who died after a balcony collapsed at a US apartment block.