The owner of a mansion rented out on AirBnb in San Francisco where four people were killed and several others were injured during a mass shooting saw the party unfold over the home's security cameras and called police to check on his house.

Police officers were on their way to issue a noise complaint at the mansion in the  100 block of Lucille Way in Orinda - a quiet, affluent community of 18,000 in the Bay Area - at around 11pm on Thursday, where more than 100 young people had been partying in a rented property. 

While on their way there, a person sent a volley of bullets into the crowd of college students, killing four and injuring several others. The identities of the victims have not been released by authorities.   

The owner, Michael Wang - who has purchased the property about a year -  told the San Francisco Chronicle that the party's host had said she was holding a family reunion for 12 people. 

However, the 58-year-old told the San Francisco Chronicle that when upset neighbors started calling him about the noise, he looked on this security camera to see far more than a dozen people. 

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Instead, nearly 100 college students had congregated in the home. 

'We called the police. They were on the way to go there to stop them, but before we got there the neighbor already sent us a message saying there was a shooting,' he said. 

'When we arrived there the police were already there.' 

The officers who arrived at the chaotic scene described feeling overwhelmed by the sheer numbers at the chaotic house party, where four revelers were shot dead and others staggered around with gunshot wounds, according to KTVU.     

The Contra Costa Sheriff's Office said in a press release three of the fatally wounded revelers died at the scene, and one was pronounced dead at John Muir Medical Center.  

A hospital spokesperson said one shooting victim was listed in critical condition, another in serious condition, and a third was treated and released.  

The statement from the sheriff's office said the exact number of injured party goers is unknown 'as some victims transported themselves to the hospital.' 

The station KQED reported on Friday that Sheriff's Office spokesman Jimmy Lee said police are still searching for the gunman.     

The event had been advertised on Instagram as an 'AirBNB mansion party,' according to East Bay Times, with a flyer asking guests to 'DM for location, BYOB [bring your own booze] and BYOW [bring your own weed].' 

Footage uploaded to Instagram moments before the shooting erupted purported to show revelers smoking joints, dancing and others in Halloween costumes at the colossal property in suburban Oakland.

Airbnb released a statement to KQED, saying:'we are horrified by this tragedy and are in close communication with Chief David Cook of Orinda Police to offer our support with his investigation into who committed this senseless violence.

'Additionally, we have taken action to ban the booking guest from our platform. Our thoughts are with the loved ones of the victims of this abhorrent act as well as the neighbors of the home.' 

Numerous emergency vehicles were on the scene and victims could be seen being carted into the back of at least six ambulances.

Local media said some of the attendees had been injured as they bolted over balconies and down stairs at the property.  

Broadcast footage showed some of the revelers limping away while police talked to others sat on the ground. 

Some of the victims were rushed to the nearby John Muir Health Urgent Care Center for treatment. There is no word on their conditions at this time.  

NBC Bay Area reported that a mother and father arrived on the scene seeking information from the police about their daughter, who they have heard had been shot dead.   

A neighbor said he heard cracks of gunfire in the house and later talked to the homeowner who said it had been rented out through Airbnb. 

Contra Costa County Sheriff's office tweeted early Friday morning: 'Orinda homicide update - four fatalities, several injuries. More details coming.' 

An Instagram post had advertised the party's location as Orinda County, saying that they planned to record a music video and said doors would open at 10pm.

Witnesses said the students at the party were from Laney College, NBC reported. 

A dispatcher at the sheriff's office said the public information officer would release more information later this morning, but he did not provide a time.

There were no details revealed over arrests.

The news follows a mass shooting that left three dead and nine others wounded in Long Beach on Tuesday at another Halloween party in California. 

Three men aged in their 20s were found dead in the backyard of a house behind a nail salon.

Five other victims were taken to hospital with life-threatening injuries and another four were also later transported to hospital.  

Witnesses said people wearing costumes were seen limping out of the building following the attack.

Orinda is located about 17 miles northeast from San Francisco. It was ranked the second-friendliest town in America by Forbes in 2012. 

Commenters on Twitter expressed shock that the mass shooting took place in Orinda, which is considered one of the safest cities in the Bay Area.  

According to local crime statistics, between 2004-2018, only one murder was reported in Orinda.