Policing are responding to a shooting at the YouTube space in San Bruno.
Some employees were able to escape the building and an unknown number of victims have been taken to San Francisco General Hospital.
Twitter was used to by trapped YouTube employees to communicate with authorities, one staffer Tweeted, “First thought it was earthquake … [then] I looked down and saw blood drips on the floor and stairs.”
It has been reported by police the shooter was female and is now dead.