US engineers investigating a balcony collapse in California that killed six people and injured seven others say water damage may have caused the structure to give way.

The incident happened during a 21^st birthday party in the early hours of Tuesday in the city of Berkeley.

Authorities said 13 people were on the fourth-floor balcony when it collapsed.

The victims were mostly Irish students who were living temporarily in the US

The victims were mostly Irish students who were living temporarily in the US as part of a work exchange programme.

An initial investigation found that the balcony support's wooden beams may not have been sealed properly at the time of construction, Berkeley Mayor Tom Bates said.

"More than likely, it was caused by rain and water damage," Mr Bates said.