A shooter opened fire at the YouTube headquarters in California on Wednesday morning (NZ Time), wounding multiple people before turning the gun on herself.
ABC7 News reported the shooter was a "white, adult female wearing a dark top and head scarf".
San Bruno Police Chief Ed Barberini told media that one person, believed to be the shooter, was found dead of a self-inflicted gunshot wound.
Witnesses told KTVU that the suspect shot her boyfriend before killing herself.
A spokesperson for the San Francisco General Hospital told local media the hospital has received patients from the incident. Four people are believed to have been injured.
"Active shooter at YouTube HQ. Heard shots and saw people running while at my desk. Now barricaded inside a room with coworkers," says one worker.
A YouTube product manager described seeing "blood drips on the floor and stairs" as he fled.
Images posted to social media show workers being brought out of the building with their hands up.
The shooter was reportedly wearing "full body armour" as she fired her weapon, according to messages in a WhatsApp group.
Police are warning the public to avoid the area.