Authorities were called to YouTube headquarters in San Bruno, San Francisco, following reports of an "active shooting" inside the facility.
International media reported multiple gunshots were heard just before 1pm local time and employees were being evacuated from the building.
San Bruno Police Chief Ed Barberini said one female was found deceased with "self-inflicted" gunshot wounds during a Police search of the building. It is believed she was the shooter.
A spokesperson for San Francisco General Hospital told CBS it had received three patients including a 36-year-old man in critical condition, a 32-year-old woman in serious condition and a 27-year-old woman in stable condition.