BERKELEY, California -- An apartment balcony collapsed during a birthday party attended by Irish students near the University of California-Berkeley early Tuesday, killing six of the 13 people who fell from the fourth-floor structure, officials said.
All of those who fell from the balcony at the Library Gardens Apartments were Irish citizens and "for the most part students," gathered to celebrate someone's 21st birthday, Irish Foreign Minister Charlie Flanagan said Tuesday.
Besides those who died, at least seven were taken to hospitals with serious injuries after the balcony gave way at about 12:40 a.m., Berkeley police Officer Byron White told CNN.
It wasn't immediately clear what caused the balcony to collapse, Berkeley police spokeswoman Jennifer Coats said.
The balcony appeared to have torn away from the rest of the building. Hours after the collapse, the fourth-floor railing -- its base gone -- was resting upside down on the railing of the balcony below, video from CNN affiliate KGO showed.
The complex is about three blocks from the University of California campus. Flanagan didn't say where the students had been going to school, but said they were in the United States on J-1 visas, which give students the chance to live and work in the country for a short period.
California authorities have contacted some of the families in Ireland about the collapse, Flanagan said.
Government officials in both Ireland and the United States reacted with sorrow.
"We mourn the tragic loss of young lives in California this morning," Irish Prime Minister Enda Kenny posted on Twitter on Tuesday.
The U.S. ambassador to Ireland, Kevin O'Malley, released a statement offering his sympathy to the relatives and friends of those who died.
Flanagan offered his condolences to the victims' relatives in a statement released by his office. He said his department would provide consular assistance to the Irish citizens involved.
Irish President Michael Higgins expressed "greatest sadness," saying he learned of the incident while on an official visit to Italy.
"My heart goes out to the families and loved ones of all those involved," Higgins said.
CNN's Laura Smith-Spark and Sheena Jones contributed to this report.
