SAN BRUNO • A woman who had voiced complaints online about YouTube opened fire with a handgun at the technology company's headquarters near San Francisco on Tuesday, wounding three people before shooting herself dead, said the authorities and media.
It was the latest in a string of mass shootings in the United States in recent years. Most recently, the massacre of 17 people at a Florida high school has led to calls for tighter curbs on gun ownership.
Police said 39-year-old Nasim Najafi Aghdam from San Diego was behind the shooting at YouTube's offices in Silicon Valley, south of San Francisco, where the company owned by Alphabet's Google employs nearly 2,000 people.
She approached an outdoor patio and dining courtyard on the premises around lunchtime, and began to fire before entering the building, police said.
A man was in critical condition and two women were seriously wounded in the attack, which ended when Aghdam shot and killed herself.
"The San Bruno Police Department is investigating a motive for this shooting. At this time, there is no evidence that the shooter knew the victims of this shooting or that individuals were specifically targeted," police said in a statement.
The website NasimeSabz.com, which Aghdam ran, had several posts about Persian culture and veganism, interspersed with screeds against YouTube. Those complaints included claims that the company was not sharing enough revenue with people who create videos for the platform.
"There is no equal growth opportunity on YouTube, or any other video-sharing site, your channel will grow if they want (it) to," read one posting on the site.
A US government security official told Reuters there was no known connection to terrorism.
YouTube product manager Todd Sherman described the shooting on Twitter, saying he heard people running and at first thought it was an earthquake before he was told that a person had a gun.
"At that point, every new person I saw was a potential shooter. Someone else said that the person shot out the back doors and then shot themselves," Mr Sherman said in his tweet.
In a recording of a 911 call posted online by the Los Angeles Times, a dispatcher can be heard saying: "Shooter. Another party said they spotted someone with a gun. Suspect came from the back patio... Again, we have a report of a subject with a gun. They heard seven or eight shots being fired."
Dozens of emergency vehicles quickly converged on the YouTube headquarters, and police could be seen in televised aerial video footage systematically frisking several employees leaving the area with their hands raised.
One victim, a 36-year-old man, was listed as being in critical condition at the San Francisco General Hospital. A 32-year-old woman was described as being in serious condition, and a 27-year-old woman in fair condition.
The authorities did not release the names of the victims.
A fourth person was taken to a local hospital with an ankle injury from fleeing the scene.
"It is with great sadness that I tell you... four people were injured in this horrific act of violence," Google chief executive officer Sundar Pichai said in letter to employees posted on Twitter.
"I know a lot of you are in shock right now. Over the coming days, we will continue to provide support to help everyone in our Google family heal from this unimaginable tragedy."
US President Donald Trump said on Twitter that he had been briefed about the shooting.
"Our thoughts and prayers are with everybody involved," Mr Trump tweeted. "Thank you to our phenomenal law enforcement officers and first responders that are currently on the scene."