Mass shooting

CEO Brian Chesky said in a tweet the company would take steps to "combat unauthorized parties and get rid of abusive host and guest conduct".

"We must do better, and we will. This is unacceptable," Mr Chesky added.

Three people died at the house, in the city of Orinda, near San Francisco, and two more died later in hospital.

City manager Dave Hansen said the victims - 11 local authority workers and one contractor - "leave a void we will never be able to fill".

The gunman shot indiscriminately before dying in a gun battle with police.

He has been identified as DeWayne Craddock and described by police as a disgruntled city employee.

Authorities said they would only refer to him by name once, in order to focus attention on the victims.

Witnesses told local media there were several casualties inside the building. Police have warned people to avoid the area.

Christchurch hospital and all of the city's schools have been placed on lockdown.

Eyewitnesses have reported running for their lives to escape a shooter.

Mohan Ibrahim told the New Zealand Herald: "At first we thought it was an electric shock but then all these people started running.

"I still have friends inside.

"I have been calling my friends but there are many I haven't heard from. I am scared for my friends lives."

Terrified survivors — who moments before were laughing and dancing with friends — described how the gunman raked the club with bullets, prompting a police SWAT team to storm the venue.

"We have cleared the building, and it is with great sadness that I share we have not 20, but 50 casualties in addition to the shooter," Mayor Buddy Dyer told a mid-morning news briefing in Orlando, more than doubling the previously given death toll.

"There are another 53 that are hospitalised."