A woman opened fire at the YouTube headquarters in San Bruno, Calif., wounding four people before taking her own life and causing widespread panic into the technology hub south of San Francisco.

San Bruno Police Chief Ed Barberini told reporters Tuesday afternoon that one person, believed to be the shooter, was found dead of a self-inflicted gunshot wound. Four other people were taken to area hospitals for medical treatment, according to Barberini.

Lisa Kim, a spokeswoman for Stanford Medical Center, said at least four patients from the shooting were expected to be admitted at the medical center.

“We do not know their conditions,” she said.

Brent Andrew, a spokesman for Zuckerberg San Francisco General Hospital and Trauma Center, said the hospital had “received several patients” and was expecting more.

Several YouTube employees sent tweets Tuesday afternoon, saying people were racing out of the company’s Cherry Avenue offices shortly after 1 p.m.

In a tweet, President Trump offered his “thoughts and prayers” to everyone involved in the incident Tuesday afternoon.

Was just briefed on the shooting at YouTube’s HQ in San Bruno, California. Our thoughts and prayers are with everybody involved. Thank you to our phenomenal Law Enforcement Officers and First Responders that are currently on the scene.

— Donald J. Trump (@realDonaldTrump) April 3, 2018

So far authorities do not believe this was an act of terrorism and appears instead to have been a case of domestic or workplace violence — although the investigation has just begun.

Witnesses in the area said they saw dozens of firefighters and police officers descending on the area. Other witnesses said they saw police holding rifles and other weapons.

The first reports of a shooting came in to San Mateo County dispatchers before 1 p.m., according to recorded traffic posted online by Broadcastify.com.

“Shooter. Another party said they spotted someone with a gun. Suspect came from the back patio,” the dispatcher said, according to scanner traffic posted online. “Address is 901 Cherry Avenue. … Again we have a report of a subject with a gun, they heard seven or eight shots being fired. This would be from the YouTube building.”

As the reports began to flood dispatchers, a sergeant was heard on the radio taking the call. He told other officers responding or monitoring the situation “to wear their gear.”

Video from the scene showed people holding their hands over their heads as they left the building, which is located in a suburb south of San Francisco. An employee told the Los Angeles Times that three YouTube buildings — 900, 901 and 1000 Cherry Avenue — had been placed on lockdown.

Producers from YouTube tweeted that they believed there was an active shooter on the company’s campus. Some said they heard so many people running that they believed an earthquake had struck. Others described a gruesome scene.

“I looked down and saw blood drips on the floor and stairs,” Todd Sherman, a YouTube producer, wrote on Twitter. “Peaked around for threats and then we headed downstairs and out the front.”

Lucacio Simoes, 40, an Uber driver from San Bruno, learned about the shooting when a friend texted him about it while he was having lunch at the nearby Tanforan shopping center. Simoes said he drove his Ford Explorer toward YouTube headquarters to see if he could help.

“There were people running down the street,” he said.

Simoes said he turned off the Uber app and start to pick people up from the street who looked like they needed help.

“I just opened the door and asked if they needed help. I was getting people away from YouTube. At one point I had seven people in the car. I picked up one man from Sneath Lane and when he got in the car he just started crying. He was in shock.”

Simoes said he dropped people off at the Tanforan Mall and on El Camino, and had performed at least six such rides Tuesday afternoon.

Michelle Tam, a hostess at the Hashes & Brews restaurant about a block away from the company’s headquarters, said a swarm of police and fire vehicles drove into the area around 12:45 p.m.

“We see lots cops and firefighters,” Tam said. “We can’t see any people. It’s just a lot of trucks along the street at the moment.”

Tam said three YouTube employees came into the restaurant appearing visibly shaken.

“They came in from a back door,” she said. “They sat down at a table. They were in a daze. One guy, there was a little blood on his head.”

One employee had a partial fragment of a bullet in her shoe, Tam said.

At another nearby business, roughly two dozen customers barricaded themselves inside Nueve restaurant around 1 p.m., when authorities told them to “stay far away from YouTube,” bartender Carlos Gutierrez told a reporter over the phone.

“Is this really happening, or is it a false alarm?” Gutierrez wondered aloud as he and others huddled near the bar.

Times staff writers Joseph Serna and Hailey Branson-Potts contributed to this story.

UPDATES:

3:05 p.m.: This article was updated with comments from President Trump and a witness.

2:40 p.m.: This article was updated with information from San Bruno Police Chief Ed Barberini.

2:10 p.m.: This article was updated with details from police radio calls.

1:50 p.m.: This article was updated to say that law enforcement sources described the shooter as a woman.

1:35 p.m.: This article was updated with additional comments from the scene.