Subscribe to Breaking News emailsYou have successfully subscribed to the Breaking News email.Subscribe today to be the first to to know about breaking news and special reports.Breaking News EmailsGet breaking news alerts and special reports. The news and stories that matter, delivered weekday mornings.A woman opened fire at YouTube’s California headquarters Tuesday afternoon before apparently turning the gun on herself, authorities said. Three other people were shot, at least one of whom was in critical condition.Breaking News EmailsGet breaking news alerts and special reports. The news and stories that matter, delivered weekday mornings.Zuckerberg San Francisco General Hospital said it received three patients with gunshot wounds: a 36-year-old man who was in critical condition, a 32-year-old woman who was in serious condition and a 27-year-old woman who was in fair condition. A fourth person was treated at Kaiser Permanente South San Francisco Medical Center for a broken ankle, the hospital said..”Once again, we are confronted with the specter of a mass-casualty situation here in the city and county of San Francisco,” Andre Campbell, a surgeon at Zuckerberg, told reporters. “This is unfortunate, and it continues. You’d think that after we’ve seen Las Vegas, Parkland, the Pulse nightclub shooting that we would see an end to this, but we have not.”San Bruno Police Chief Ed Barberini said the shooter appeared to have killed herself.”It was very chaotic, as you can imagine,” Barberini said.Senior law enforcement officials said the woman, who appeared to be in her 30s, approached an outdoor patio and dining area near lunchtime and opened fire. They said the shooting appeared to have stemmed from a domestic dispute and wasn’t related to terrorism.Earlier, YouTube employees tweeted that they had evacuated the building in San Bruno, south of San Francisco, or were in hiding.Active shooter at YouTube HQ. Heard shots and saw people running while at my desk. Now barricaded inside a room with cookers.— Vadim Lavrusik (@Lavrusik) April 3, 2018I am behind another building with colleagues. There are helicopters. There are lots of police nearby. I don’t know if the shooter has been found. If you hear they’ve been found, tell me. I’m safe for now, but don’t feel safe until they’ve been found.— Lil | Milktea (@_lilchen) April 3, 2018 Barberini said San Bruno police began receiving multiple 911 calls of an “active shooter” at 12:46 p.m. (3:46 p.m. ET) and were on the scene within two minutes. The federal Bureau of Alcohol, Tobacco, Firearms and Explosives and the FBI said they also responded to the scene.Ricardo Luis Horna, 29, a development specialist for YouTube, said he saw his colleagues running and falling down a hill as security officers told everyone to evacuate.”There was chaos in the parking lot,” Horna said in an interview. “People were running to their cars.”Marco Tartaglia, who works at Walmart eCommerce headquarters near the complex on Cherry Street, told NBC Bay Area that he heard about 15 shots “from the direction of the YouTube building, from what sounded like inside.””We heard the shots first, and that immediately drew us over to the window to see what the heck’s going on, and next thing you know, you see people streaming out, just running, dozens of them, just running out the front exit,” Tartaglia said.Google, YouTube’s parent company, said it was coordinating with authorities.President Donald Trump was briefed on the incident, said Michael Anton, a spokesman for the National Security Council.CORRECTION (April 3, 2018, 7:36 p.m. ET): An earlier version of this article misidentified the job site of Marco Tartaglia. He works at Walmart eCommerce headquarters, not at a Walmart store.Breaking News EmailsGet breaking news alerts and special reports. The news and stories that matter, delivered weekday mornings.ContributorsRima Abdelkader, Tom Winter, Jonathan DienstMORE FROM newsHave feedback?How likely are you to recommend nbcnews.com to a friend or colleague?0 = Very unlikely10 = Very likelyPlease select answerIs your feedback about:ContentDesignOtherPlease select answerLeave your email if you’d like us to respond. (Optional)Please enter a valid email addressThank you!Your feedback has been sent out. Please enjoy more of our content.We appreciate your help making nbcnews.com a better place.