Police in Northern California say they are responding to an incident involving an “active shooter” at YouTube headquarters.
Gunshots were reported at the company’s campus in San Bruno, south of San Francisco.
Ambulances are at the scene and authorities have warned the public to stay out of the area.
Google, which owns YouTube, has said it is investigating a possible “gunfire incident”.
Unconfirmed reports from local media say the shooter is a woman.
Zuckerberg San Francisco General Hospital has said it is treating patients from the incident. No details were provided on their condition.
The Stanford Health Care health system has said it is treating four to five people from the shooting, ABC News reports.
One employee at a nearby fast food restaurant told Fox station KTVU he had treated a young woman who suffered a gunshot wound to the leg. He said he had fashioned a makeshift tourniquet from a bungee cord as they waited for first responders.
Some of the injured were reportedly hurt as they fled the building.