Several YouTube employees tweeted about hearing shots fired in the building. Google Chief Executive Officer Sundar Pichai said in a statement that employees were having lunch around 12:45 p.m. when the first reports came in about the shooting.
At a press conference, the San Bruno Police Department reports that within minutes officers arrived at the headquarters as people fled through the front doors and away from the scene of the shooting in an outdoor courtyard.
In a statement released Wednesday, YouTube reports Nasim Aghdam gained access to the campus through the parking garage but could not get into the building. She was armed with a handgun.
After officers arrived at the scene YouTube employees helped them get into the building and some helped those who were wounded, according to YouTube's statement.
Three people were shot by Aghdam and were hospitalized at Zuckerberg San Francisco General Hospital. They include a 36-year-old in critical condition, a 32-year-old woman in serious condition and a 27-year-old woman in fair condition. An additional person sustained an ankle injury while fleeing the scene, Barberini said.
Aghdam died after turning the gun on herself, according to San Bruno Police Chief Ed Barberini.
On Aghdam's social media accounts she called YouTube a "dictatorship" and claimed on her own site that it had "filtered [her] channels to keep them from getting views."
She also identified herself as vegan and an animal rights activist. Before her channel was taken down around 8 p.m. Tuesday it included playlists about animal cruelty and vegan cooking.
The Associated Press reports law enforcement officials say they are investigating the shooting as a domestic dispute.
Police continue to search the campus and will continue their investigation overnight. There was no threat to the campus and the nearby community as of 4:30 p.m., according to the police department.
President Donald Trump tweeted that he had been briefed on the shooting.
"I know a lot of you are in shock right now. Over the coming days, we will continue to provide support to help everyone in our Google family heal from this unimaginable tragedy," Pichai wrote in a statement.
Stay with FOX40 for the latest as this story develops.