BLOOD ON FLOOR: Shooter 'down' at YouTube

AT least four people were wounded and the suspected shooter, a woman, was found dead at YouTube headquarters in San Bruno, California.

San Bruno Police Chief Ed Barberini told reporters the deceased woman had died of an apparent self-inflicted gunshot wound.

The shooter earlier stormed the offices of YouTube prompting terrified workers to run for their lives.

The headquarters in San Bruno, California was placed on lockdown after police swarmed the area following reports of shots being fired.

The shooting is believed to have begun after the woman had a dispute with her boyfriend during an outdoor party on the campus.

Multiple law enforcement sources told NBC News the shooter is female and is now down.

A witness has told of discovering a bloodied victim in a carpark.

"She had a leg injury, a gunshot wound, so I put a tourniquet on her to try to help her," the witness told Sky News. He said the victim was an Asian woman, aged in her 20s.

YouTube is owned by Google whose main headquarters are based in northern California.

In a tweet, the company confirmed it was working with authorities and will provide information as soon as it has become available.

A spokesman for San Francisco General Hospital said the facility is receiving patients but would not confirm how many, CBS News reported.

However Stanford Health Care Hospital said it has received four to five patients following the shooting, according to Sky News.

A law enforcement source told ABC7 News that the shooter is a white, adult female wearing a dark top and headscarf.

A second law enforcement official also said the shooter is a woman.

The shooting is believed to have begun after the woman had a dispute with her boyfriend during an outdoor party on the campus.

Police and emergency services responded to the "active scene" after multiple emergency calls were received. 

Shots were heard from inside the offices as well as the surrounding area, a San Bruno city manager told Buzzfeed News.

The San Bruno Police tweeted at 1pm local time advising people to avoid the area, reports KRON4.

There are also unconfirmed reports that the suspect has shot themselves.

Worker Vadim Lavrusik tweeted: "Active shooter at YouTube HQ. Heard shots and saw people running while at my desk. Now barricaded inside a room with coworkers.

YouTube parent company Google tweeted: "YouTube situation, we are coordinating with authorities and will provide official information here from Google and YouTube as it becomes available."

YouTube product manager Todd Sherman said they were sitting in a meeting when they heard people running and felt the floor rumbling. "First thought it was an earthquake," he wrote on Twitter.

"We headed towards the exit and then saw more people and someone said that there was a person with a gun.

"At that point every new person I saw was a potential shooter. Someone else said that the person shot out the back doors and then shot themselves," he wrote.

He said he saw blood on the floors and stairs.

Images posted on social media show YouTube employees being evacuated from the building with their hands above their heads.

There are reports that helicopters and tactical teams have arrived at the scene.