Authorities didn't disclose their conditions.
The company that owns the world's biggest online video website said Tuesday on Twitter that it's advising employees and others to stay away from the area and that it's set up a help line for workers.
Earlier in the afternoon, Vadim Lavrusik, product manager at YouTube, tweeted that he heard shots and saw people running while at his desk around 1 p.m.
The department tweeted a map of 901 Cherry Avenue and asked the public to stay away from the area.
"After existing the room we still didn't know what was going on but more people were running". He said he got out of the building safe and was in an Uber headed home.
A witness told KRON4's Gabe Slate that they heard 20 shots fired. He was at a Carl's Jr. fast-food restaurant across the street from an end of the YouTube building where there are tables with umbrellas on a patio. Michael used a bungee cord as a tourniquet around the woman's leg. People at the fast-food restaurant tried to use napkins to stop the bleeding.
Authorities were seen taking extra precautions as they evacuated the building, frisking every individual before they were allowed to move on to safety.
Several years ago 800 people worked at the building. Originally created in 2005, YouTube is one of the most popular sites on the web. It was unclear if she is a YouTube employee. The Bureau of Alcohol, Tobacco, Firearms and Explosives says it's also responding to the shooting at YouTube's suburban campus.
San Bruno is around 17km south of San Francisco.
Northern California's Stanford Hospital said it has received four to five patients, but a hospital spokeswoman did not have information on their conditions or their wounds. Their conditions are unknown.
Almost 3,000 people work at the headquarters, which are located about 12 miles south of downtown San Francisco.
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