San Francisco General Hospital spokesman Brent Andrew said the hospital received patients from the incident but could not confirm a number.
Stanford Medical Center said it is expecting 4 to 5 patients. Multiple 911 calls reported gunfire, and police and fire officials swarmed the area, City Manager Connie Jackson said.
City Manager Connie Jackson says there have been multiple 911 calls reporting a shooting and that police and fire officials have responded.
Police and federal agents converged Tuesday on YouTube's headquarters in the San Francisco Bay Area after receiving numerous reports of a shooting.
The San Bruno Police Department said in multiple tweets they were "responding to an active shooter" at 901 Cherry Avenue, where the Google-owned video platform is headquartered. "Now barricaded inside a room with coworkers", tweeted the employee, Vadim Lavrusik.
"We heard the shots first, and that immediately drew us over to the window to see what the heck's going on, and next thing you know, you see people streaming out just running, dozens of them, just running out the front exit", Marco Tartaglia said.
Police say a woman believed to be the hooter at YouTube headquarters is dead of self-inflicted gunshot.
"I think there might be a shooter in my building", read one text.
"We are responding to an active shooter".
He said he was safe and on his way home. Hudson said he's become used to hearing about gun violence but has never been so close to it before. It feels like it could really be anyone.
Calls and emails to YouTube representatives seeking comment were not immediately returned.
YouTube headquarters is located some 50 kilometres from the main Google campus in Mountain View.
In the last few minutes the San Bruno Police promised a statement at 2:30pm local time.
One image posted by a Twitter user showed employees being led out of the building with their hands up, with no further explanation.
This story is developing and will be updated.