At least four people were shot at YouTube’s headquarters in San Bruno on Tuesday, according to a police spokesman. Three victims were taken to local hospitals. A fourth person died at the scene, apparently of a self-inflicted gunshot wound, police said during a press conference Tuesday afternoon.

Shooting victims included a 36-year-old male in critical condition, a 32-year-old woman in serious condition, and a 27-year-old woman in fair condition, according to Zuckerberg San Francisco General Hospital spokesman Brent Andrew. Another woman present at the shooting was treated for a twisted ankle at Kaiser Permanente South San Francisco Medical Center, a spokesman said.

The shooting suspect was a woman, San Bruno Police Chief Ed Barberini said, and CNBC later reported she has been identified as Nasim Najafi Aghdam, 39. Police said she was the person who died at the scene. According to NBC Bay Area, Aghdam had posted a video on YouTube in January claiming that the video site “discriminated and filtered” her content.

Several hundred employees were evacuated on Tuesday afternoon after the shooting began. “It’s with great sadness that I tell you — based on the latest information — four people were injured in this horrific act of violence,” Google CEO Sundar Pichai said in a note to employees. “We’re doing everything we can to support them and their families at this time.”

Vadim Lavrusik, a product manager at the company, tweeted that there is an active shooter on campus. The San Bruno Police Department instructed people to stay away from 901 Cherry Avenue, where the company is located. Multiple 911 calls have been received from inside the building, according to a report from local news station KRON.

We are responding to an active shooter. Please stay away from Cherry Ave & Bay Hill Drive. — San Bruno Police (@SanBrunoPolice) April 3, 2018

The shooting began at around 12:45PM PT, when many people were eating on a patio in the rear of the building, according to police. In a Twitter thread, YouTube product manager Todd Sherman said that employees first thought there had been an earthquake. People began running out of their meetings, he said, but before reaching the exit, they got word that someone had a gun. Sherman said he saw blood on the floor and the stairs. He also said the shooter may have committed suicide.

Footage posted on Snapchat showed YouTube employees streaming out of the building with their hands above their heads. Police also blocked off the San Bruno Ave. exit of Interstate 280 as the investigation got underway on Tuesday afternoon.

As one of the most-visited services on the web, YouTube is under constant scrutiny for its policy decisions over content moderation, monetization, and other issues. Last month, the company updated its policy on videos featuring firearms, expanding the list of accessories that cannot be featured in videos that sell them or instruct users how to manufacture or install the accessories.

Shannon Liao, Rachel Becker, and Sam Byford contributed to this report.

Update April 3rd, 7:37PM ET: This article has been updated to include a statement from Google CEO Sundar Pichai.

We were sitting in a meeting and then we heard people running because it was rumbling the floor. First thought was earthquake. https://t.co/gmolQmRXm1 — Todd Sherman (@tdd) April 3, 2018

Active shooter at YouTube HQ. Heard shots and saw people running while at my desk. Now barricaded inside a room with coworkers. — Vadim Lavrusik (@Lavrusik) April 3, 2018

Myself, and my entire team in San Bruno, are okay. Thank you for checking on all of us. If you believe in prayer, please keep our colleagues in mind. — Ryan Wyatt (@Fwiz) April 3, 2018

We are seeing @YouTube employees being brought out with hands up! pic.twitter.com/ZlSMY9FIVm — Erin (@erinjeanc) April 3, 2018

Police activity at 901 Cherry Ave, please stay out of the area. pic.twitter.com/H6iAj0g7ra — San Bruno Police (@SanBrunoPolice) April 3, 2018

From everyone at Apple, we send our sympathy and support to the team at YouTube and Google, especially the victims and their families. — Tim Cook (@tim_cook) April 3, 2018