Police in Northern California are responding to reports of a shooting at YouTube headquarters in the city of San Bruno.
A law enforcement source told ABC7 News that the shooter is a white, adult female wearing a dark top and headscarf.
Authorities say a woman believed to be the shooter is dead of a self-inflicted gunshot and four other people have been wounded.
On Twitter, YouTube employees reported hearing multiple gun shots inside the campus.
One victim has been shot in the chest although no fatalities have been confirmed, reports ABC7News.
Google, which owns YouTube, said in a statement that it is coordinating with authorities.
TV helicopter video shows officers patting down people grouped outside a building and police vehicles surrounding the area.
Earlier, several YouTube employees posted on social media that they heard gunshots and took cover inside before fleeing the building.
Zuckerberg San Francisco General Hospital spokesman Brent Andrew said that facility received three patients: two women and a 36-year-old man.
Officers rushed to the San Bruno offices after receiving a string of 911 calls about an active shooter around 12:45 p.m.
YouTube employee Vadim Lavrusik was one of the first to reveal a shooter was on the loose, stating how staff had barricaded themselves inside the San Bruno offices.
"Was just briefed on the shooting at YouTube's headquarters in San Bruno, California", President Donald Trump tweeted.
He couldn't provide details on any possible weapons used or any new information on the shooter. "The fire alarm went off so we started to evacuate and then people (started) running saying there was a shooter".
The Bureau of Alcohol, Tobacco, Firearms and Explosives also said it responded to the shooting at YouTube's suburban campus.