Police are responding to an “active shooter” near YouTube headquarters, according to the department’s Twitter feed, and have asked people to stay away from the area.

YouTube employees tweeted that he had heard shots fired. According to KPIX, a CBS affiliate, there have been multiple injuries. Brent Andrew, chief communications officer for Zuckerberg San Francisco Hospital, confirmed that people had been transported to the hospital from YouTube headquarters, but didn’t have an exact amount. “We don’t have any numbers yet, but we’re expecting more,” he said.

According to news reports, the shooter was a woman and is now dead. 

A YouTube employee contacted by CNET said he couldn’t talk and abruptly hung up. Google, YouTube’s parent company, said it’s coordinating with authorities.

At the scene, there were at least three helicopters overhead and a heavy police presence. Interstate 280, a nearby freeway, was shut down as well.  

A witness inside a nearby Walmart eCommerce Corporate headquarters told CNET his building had been locked down as well. He said employees had been instructed to stay away from windows. He said what appeared to be SWAT team members entered the YouTube building with guns drawn and quarantined the area. “Dozens of cop cars, ambulance fire trucks and swat trucks. 20-30 or so total,” he said in a text.

A Walmart spokesperson wasn’t immediately available for comment.

The Google subsidiary is the largest online video site on the planet, with more than a billion visitors a month.

This is a developing story …

Update, 1:33 p.m. PT: Adds new details.

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