SAN BRUNO, Calif. (AP) — A woman opened fire at YouTube headquarters Tuesday, setting off a panic among employees and wounding at least four people before fatally shooting herself, police and witnesses said.

Officers and federal agents swarmed the company's complex in the Bay Area city of San Bruno after receiving multiple 911 calls reporting gunfire.

Television news footage showed people leaving the building in a line, holding their arms in the air. Officers patted them down to make sure none had weapons.

The shooting left "four victims who have all been transported for gunshot related injuries and we have one subject who is deceased inside the building who we believe to be the shooter," said San Bruno Police Chief Ed Barberini.

YouTube employee Vadim Lavrusik posted on Twitter that he heard gunshots and saw people running. He said he was barricaded in a room with co-workers before being safely evacuated.

Will Hudson said a friend who works for YouTube texted him about the shooter.

"I think there might be a shooter in my building," read one text. "The fire alarm went off so we started to evacuate and then people (started) running saying there was a shooter."

San Francisco General Hospital received three patients: a 36-year-old man in critical condition, a 32-year-old woman in serious condition and a 27-year-old woman in fair condition, a spokesman said.

The hospital said later that it did not expect to receive more patients. It was not immediately clear where the fourth gunshot victim had been sent for treatment.

Google, which owns the world's biggest online video website, posted on Twitter that the company was coordinating with authorities. The Bureau of Alcohol, Tobacco, Firearms and Explosives said it also responded.

The White House said President Donald Trump was briefed on a shooting and that officials were monitoring developments.

Hudson said his friend made it safely back to San Francisco and was in contact with his family. Hudson said he's become used to hearing about gun violence but has never been so close to it.

"It just feels strange. It feels like it could really be anyone. That's really the strangeness of it," he said.

Calls and emails to YouTube representatives were not immediately return