San Francisco - Police said on Tuesday they were responding to an "active shooter" at the headquarters of YouTube in San Bruno, California.
Police in the city south of San Francisco warned people in a Twitter message to stay away from the address where YouTube, owned by Alphabet Inc's Google, is based.
"We are responding to an active shooter. Please stay away from Cherry Ave & Bay Hill Drive," San Bruno police said on Twitter.
A police dispatcher said by telephone that it was an "active situation," declining to elaborate.
"Active shooter at YouTube HQ. Heard shots and saw people running while at my desk. Now barricaded inside a room with coworkers," YouTube employee Vadim Lavrusik said on Twitter. He later tweeted that he was safe and had been evacuated.
"We were sitting in a meeting and then we heard people running because it was rumbling the floor. First thought was earthquake," Todd Sherman, a YouTube product manager, said on Twitter.
Local television images showed YouTube employees walking out of the building with their hands raised.