Terrified employees fled as gunfire rang out at YouTube's sprawling headquarters in San Bruno, California, on Tuesday, prompting a massive police response and evacuation as victims were transported to nearby hospitals. San Bruno Police Chief Ed Barberini said one female suspect was found dead from a self-inflicted gunshot wound. Three people were transported to local hospitals with gunshot wounds.

Barberini said police arrived on scene at 12:48 p.m. local time as encountered frantic employees fled the building. "It was very chaotic as you can imagine," he said.

Responding officers encountered one victim with a gunshot wound toward the front of the building before finding the deceased suspect, Barberini said. Several minutes later, police located two additional victims at an adjacent building.

A spokesman for San Francisco General Hospital told CBS News it has 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. 

Heavily armed police surrounded the facility, with armed SWAT vehicles stationed outside. Police officers could be seen patting down employees evacuating the campus to a nearby parking lot, where they were surrounded by police cars.

White House press secretary Sarah Sanders said President Trump has been briefed on the shooting and they are "monitoring the ongoing situation."

On Twitter, Mr. Trump offered his thoughts and prayers to those affected in the shooting.

The FBI and San Francisco Field Division of the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) said it was responding to the scene.

Several employees tweeted they heard gunfire Tuesday afternoon. Vadim Lavrusik said he barricaded himself and others inside a room before they were able to escape safely.

Google, YouTube's parent company, said in a statement that they are "coordinating with authorities and will provide official information here from Google and YouTube as it becomes available."

The headquarters is about 12 miles south of downtown San Francisco, close to San Francisco International Airport. It encompasses about 200,000 square feet, and YouTube leases the building from Gap, Inc., according to a 2017 article in the San Francisco Business Times.

Google says there are more than 1,100 employees at the office and that YouTube is San Bruno's largest employer, with a variety of people dedicated engineering and sales.

The owner of a nearby restaurant told CBS News he was outside smoking a cigarette when he heard several pops. Denny, who didn't want to give his last name, said there was a brief pause in the gunfire before it continued. He said he heard a total of about 15 to 17 shots.

"It went on for awhile, those shots, it wasn't like emptying the clip like 'boom boom boom,' it was more of a slower pace," Denny said.