SAN FRANCISCO (BLOOMBERG) - Just after noon on Tuesday, life at YouTube's campus in San Bruno, California, was thrown into chaos.
At 12.46pm, police received multiple emergency calls about an active shooter at the headquarters of the Google unit.
Officers arrived to a frantic scene, with employees pouring out of the buildings. During the lunch hour, a female shooter had opened fire and injured at least three people, before killing herself.
The shooter's identity and motive have not been confirmed.
The earliest signs came from staff at YouTube, part of Alphabet Inc's Google. They began sending out alarming messages on Twitter right after the police arrived.
Mr Todd Sherman, a YouTube product manager, wrote on Twitter that staff were running through the office halls.
"At that point every new person I saw was a potential shooter," he wrote.
Mr Sepand Parhami, a software engineer at YouTube, said he was on a patio having lunch when he heard a couple of shots fired.
"It looked to be a woman, from the person's height and stance," Mr Parhami said.
The shooter was coming from the parking garage to the lobby. Mr Parhami then scrambled for the door and went inside.
"Then the shooter started shooting at the lobby doors," Mr Parhami said. "There were drops of blood on the staircase. There were also sirens going off within the building."
He said he saw one person lying on the ground outside the lobby doors at the patio.
Visitors to YouTube's offices in San Bruno must enter with an employee or guest badge.
While there are security personnel, YouTube, like most tech companies in Silicon Valley, lacks metal detectors.
One woman who works at YouTube waited out the shooting in a second-floor conference room, one level above the attack.
She and 20 of her colleagues heard multiple shots that first sounded like banging, punctuated by sounds of running. She asked not to be identified discussing the event.
They shared their location with building security, which then notified the police, the woman said.
As they waited to be rescued, most people stood on one side of the room, away from a window that they covered with shades.
Others sheltered under the conference table until police came and escorted them out.
Mr Zach Vorhies, a YouTube software engineer, said he escaped a building on campus after seeing a heavyset man on the ground with what appeared to be a gunshot to the stomach.
Mr Vorhies said he saw a police officer coming in with an assault rifle and bolted out of the rear exit.
"I know a lot of you are in shock right now," Google Chief Executive Officer Sundar Pichai wrote in a note to employees. "Over the coming days, we will continue to provide support to help everyone in our Google family heal from this unimaginable tragedy."
Others described a frantic scene in the suburb just south of San Francisco.
Mr Charlie Chen, an employee at a nearby bank, had gone to a local Carl's Jr for lunch.
He heard at least 20 rounds of gunshots, and someone called 911.
A girl came into the restaurant with a gunshot wound to her calf. It took five to seven minutes for the ambulance to come, he said.
When the police cruisers pulled up, they arrived "with rifles ready", Mr Sherman, the YouTube manager, wrote on Twitter.
Later, he wrote that he was in an Uber cab on the way home. "Hope everyone is safe," he wrote.
Mr Sherman did not respond to requests for additional comment.
Late in the afternoon, at least eight agents of the Federal Bureau of Investigation escorted a large group of people - at least five dozen employees - off campus.