The suspected female shooter at the
Police said the woman was found dead in the building with a "self-inflicted wound."
San Bruno police had warned people on Twitter to stay away from the area housing the headquarters of the Google-owned video sharing service near San Francisco.
According to the White House, President Donald Trump is aware of the situation, adding that the administration was monitoring the incident.
Some YouTube employees recounted the ordeal on Twitter.
"We were sitting in a meeting and then we heard people running because it was rumbling the floor. First thought was earthquake," Todd Sherman tweeted.
"I looked down and saw blood drips on the floor and stairs. Peeked around for threats and then we headed downstairs and out the front."
The shooter has not been identified and motive is unknown as at the time of filing this report.
UPDATE:
Three persons are reportedly in critical condition and one dead. The shooter was said to have killed herself after shooting two women and one man.