A woman suspected of opening fire at YouTube's campus in California is dead after reportedly shooting herself. At least four people have reportedly been taken to hospital after being shot, according to police.

Police Chief Ed Barberini said during a news conference that the female victim found was "believed to be the shooter" but that police and other law enforcement agencies are continuing to investigate the "active" situation. He said at least two victims were found in a building adjacent to the main YouTube offices. At this time, police do not belive this to be an act of terrorism.

One staff member at the San Bruno campus - located 11 miles from San Francisco - said he barricaded himself in a room after hearing shots. Another reported seeing "blood drips" on the floor and stairs as he fled the building as armed police swarmed the site. Product manager Vadim Lavrusik tweeted that he "heard shots and saw people running while at my desk" but he and some colleagues have been evacuated and are safe at this time.

Mr Barberini said the buildings have been evacuated and police are questioning "a few hundred" people to "put the pieces together".

The police have advised the public to stay out of the area of the offices. Footage posted via Snapchat close to the campus shows some people walking down the street with their hands above their heads and police surrounding the building while wearing tactical gear.

Aerial footage shows scene outside YouTube HQ following reports of shooting

The San Bruno City Manager's office told BuzzFeed News that the city received several emergency calls from inside the building and the surrounding area regarding gunshots. Police are currently searching individuals who have been evacuated before allowing them to leave the scene to prevent the shooter from blending in with escaping crowds.

Police have released very little information, however, unconfirmed reports from local media said that the shooter is female, and two people are injured. Employees with shocked expressions, some of them wearing apparel with Google’s logo were leaving the scene, The Independent reported from the sprawling San Bruno campus.

YouTube HQ: West Coast Correspondent Jeremy White delivers Facebook Live from the scene

People in surrounding offices have shared some images of the scene on various social media platforms.

The video streaming company is owned by Google, whose main headquarters are also located in the northern California area. The company tweeted that it has been "coordinating with authorities and will provide official information here from Google and YouTube as it becomes available".

Todd Sherman, another YouTube staffer, tweeted that he "saw blood drips on the floor and stairs" as he was evacuating. He later tweeted that he is safe and on his way home from the scene.

The San Francisco General Hospital has taken in an unknown number of patients from the shooting incident, according to local news station KCBS. Spokesman Brent Andrew said a 36-year-old man is in critical condition, a 32-year-old woman was in serious condition, and a 27-year-old woman was in fair condition. Stanford Hospital Media Relations Spokesperson Lisa Kim has confirmed that four to five patients have been transferred to that hospital but did not comment on the nature or severity of their injuries.

Local news station KTVU spoke with an employee from the fast food restaurant Carl's Jr located next to the YouTube headquarters building. The employee, called Michael, said he helped a Chinese woman who looked to be in her 20s and been shot in the leg. It is unclear if the woman was an employee or whether she saw the shooter. "She was relaxed but scared. She wasn't in shock," he said, adding that he had used a bungee cord as a tourniquet around her wound.

Video shows people walking with their hands above their heads following YouTube shooting

A software engineer named Sepand Parhami told The Independent in San Bruno he had heard a series of pops and then “everyone started scrambling”. He recounted seeing blood on the stairs. “It was kind of a blur," he said.

The YouTube campus is home to roughly 1000 employees at any given time. It is unclear at this time if the suspected shooter was an employee or just visiting the office. It is also unknown at this time what the suspect's motive may have been and if there was any relationship between the shooter and victims.