Google, Facebook, Amazon, Microsoft, and Twitter ask employees to stay away from Silicon Valley and Seattle HQs as they bunker down against coronavirus

Twitter has also asked employees to work from home per BuzzFeed, as has CEO Jack Dorsey's fintech company Square.

Speaking to BuzzFeed, Twitter's head of human resources Jennifer Christie tried to put a positive spin on the situation.

"We'll never probably be the same, people who were reticent to work remotely will find that they really thrive that way. Managers who didn't think they could manage teams that were remote will have a different perspective. I do think we won't go back," she said.

Twitter wants all 5,000 employees to work from home, and has mandated it for any in Japan, South Korea, and Hong Kong. Dorsey has also pulled out of an appearance at the SXSW conference in Austin, Texas.

Originally Microsoft had told employees in its Seattle and San Francisco offices that they could work from home until March 9, but on Wednesday it extended that deadline to March 25.

The company will also continue to pay its 4,500 hourly workers — cafeteria workers, shuttle bus drivers — even if they work reduced hours. "This will ensure that, in Puget Sound for example, the 4,500 hourly employees who work in our facilities will continue to receive their regular wages even if their work hours are reduced," the company said.

Slack put out a statement on Thursday announcing it was encouraging staff to work from home on Friday after discovering that one of its employees had just returned from "an area with potential COVID-19 exposure while traveling overseas."

"This employee has not been confirmed to have contracted COVID-19 and has not reported any symptoms. However, because this employee was present in the office after returning from travel we are taking the following actions out of an abundance of caution," Slack said.

It said it would close its San Francisco offices over Friday afternoon and the weekend to perform a thorough deep clean.