The floor section of a damaged balcony is laid on a flatbed truck in Berkeley, California, June 16, 2015. [Photo/Agencies]

City inspectors barred use of the building's other balconies while they are checked for safety.

The Library Gardens apartment complex, completed in 2007, is in a lively part of downtown Berkeley close to the campus and is a popular place for students to live. Several tenants reached by telephone said it is well-maintained.

Berkeley Police Chief Michael Meehan said the response to the noise complaint had been given a lower priority after police received a call of shots fired elsewhere.

The building is owned by BlackRock, the largest asset-management fund in the US, according to city officials, and managed by Greystar Management, whose website says it operates more than 400,000 units in the US and abroad.

In a statement, Greystar extended condolences to the victims' families and added: "The safety of our residents is our highest priority and we will be working with an independent structural engineer and local authorities to determine the cause of the accident.''

On the closed street below, a shrine was growing: flowers, a pack of cigarettes, a Cal Berkeley banner, condolence notes. Victims' relatives were expected to begin arriving from Ireland on Tuesday night.

"My heart breaks for the parents who lost children this morning, and I can only imagine the fear in the hearts of other parents whose children are in California this summer as they seek to contact them now,'' Irish Prime Minister Enda Kenny told lawmakers in Dublin. "It is truly terrible to have such a serious and sad incident take place at the beginning of a summer of adventure and opportunity for so many young people on J-1 visas in the US.''

A 2010 Agencies investigation of the J-1 program and the companies that arrange the visits found that many students paid thousands of dollars to come to the US, only to learn the jobs they were promised didn't exist. Some had to share beds in crowded houses or filthy apartments.

Following the investigation, the State Department tightened its rules governing participating businesses.