UPDATE, 5:55 p.m. Eastern Time: In press conference on Tuesday afternoon, San Bruno Police Chief Ed Barberini confirmed that there were at least four people with gunshot wounds being treated at a nearby hospital, following a shooting at YouTube's corporate headquarters on Cherry Avenue in San Bruno, California.
Northern California's Stanford Hospital says it has received four to five patients from a shooting at YouTube headquarters.
Of those, one was a woman dead from an apparent self-inflicted gunshot wound, and is believed to be the shooter. The two women are aged 32 and 27, and are in a serious and fair condition, respectively.
One YouTube employee said during the shooting people were trying to get out of the building "as fast as they could".
Police surround YouTube headquarters in San BrunoVoorhees said he then saw a man on the ground with some sort of wound to the chest and abdomen area as the gunman stood near him. "The fire alarm went off so we started to evacuate and then people [started] running saying there was a shooter", read another chilling account.
The company that owns the world's biggest online video website said Tuesday on Twitter that it's advising employees and others to stay away from the area and that it's set up a help line for workers.
Google, which is the parent company of YouTube, said in a statement that it is coordinating with authorities and will release information as it becomes available.
The White House said President Donald Trump was briefed on a shooting at YouTube headquarters and that officials were monitoring it. Heard shots and saw people running while at my desk.
When contacted for more information, The San Mateo County Sheriff's Office informed CBS news that they were treating the situation at the YouTube HQ as an "active shooter incident" but were unable to provide any more details at this time. "I was close to the exit, so I got out of there quick".
Todd Sherman, who works as a product manger at YouTube, tweeted his entire experience inside the building. "Now barricaded inside a room with coworkers".
Sherman said he started running after hearing someone possibly had a gun.
Local TV news reports showed pictures of people leaving a building with their hands over their heads. "Thank you to our phenomenal Law Enforcement Officers and First Responders that are now on the scene", Mr Trump tweeted. San Bruno Police tweeted to avoid the area until further notice. "Someone else said that the person shot out the back doors and then shot themselves".
Live arial footage from the scene shows dozens of employees evacuating the campus with the aid of local law enforcement.