James Martin/CNET

For the most up-to-date news and information about the coronavirus pandemic, visit the WHO website

If you visit Apple's Cupertino, California, campus, with its cylinder set amid trees, bushes and walking paths, you might notice it seems a little quieter. The same goes for Twitter's offices in typically busy downtown San Francisco, or Facebook's massive open-office-plan buildings in Menlo Park.

Across Silicon Valley, companies are telling employees to work from home amid the novel coronavirus outbreak and avoid the open-office plans, gourmet meals and other perks that have become a staple of the tech world.

Apple CEO Tim Cook sent a letter to staff around the world encouraging them to work from home until March 13, Bloomberg reported over the weekend. He called the coronavirus outbreak an "unprecedented event" and a "challenging moment."

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Microsoft CEO Satya Nadella said he's committed "to making public health our top priority," encouraging employees in the Seattle and San Francisco areas to stay home until March 25. Other companies such as ride hailing company Lyft, business social network LinkedIn, chipmaker Intel and HP have made similar moves. Even Stanford University, in the heart of Silicon Valley, has canceled in-person classes.

And Facebook has canceled its F8 developer conference in San Jose, just down the road from its headquarters, citing concerns about the virus. "This was a tough call to make," Konstantinos Papamiltiadis, Facebook's director of developer platforms and programs, said in a statement last month. Google, Nvidia and the Game Developers Conference also cancelled their usually-annual gatherings.

The moves come as fear about the virus, first detected in China late last year, spreads across the globe. Tens of thousands of people have tested positive for COVID-19, the official designation for the disease caused by the new coronavirus. Researchers say it appears to be much deadlier than the flu, which itself kills tens of thousands of people in the US each year. The coronavirus appears to particularly threaten the sick and elderly.

In response, large tech conferences like Facebook's F8, SXSW in Texas, Google I/O in California and Mobile World Congress in Barcelona were canceled. US Sen. Ted Cruz from Texas and Rep. Paul Gosar of Arizona put themselves in quarantine after being exposed to the virus at a political gathering, and at least two cruise ships, including one in San Francisco, were held away from ports after initial tests indicated sick people were on board.

Cities and states are taking dramatic action as well. San Francisco has banned "nonessential group events" at any city-owned facilities until at least March 23, local CBS affiliate KPIX reported. The Los Angeles Times reported its home city has increased funding for tests amid outbreaks there.

"We have to be prepared. We have to protect the well-being of our loved ones and our neighbors," Los Angeles Mayor Eric Garcetti said last week.

Where this all will lead is unclear. Countries are still testing patients as the virus spreads. Meanwhile, lawmakers and administrators in cities and counties around Seattle and New York are encouraging companies to allow employees to work from home if they can.

Hitting business too

Coronavirus isn't just causing a public health scare, it's also slowing economic activity around the world. Stock markets have plunged as the number of cases have grown.

Tech companies in particular may be hit by the virus, as devices from Apple's iPhone to HP's printers are built with parts made throughout Asia.

Apple, which is one of the most highly valued companies in the world, said in February that it expected fewer supplies of its iPhones, which will also likely lead to lower sales. Smartphone giant Samsung has also reportedly slowed production of some devices amid coronavirus outbreaks in its home country of South Korea.

Companies like Apple, Google, Twitter and Facebook have also pledged to pay hourly workers affected by the virus. And Uber, Lyft, Doordash and Postmates are considering financial payments to help drivers, according to The Wall Street Journal.

What's unclear is how long this will continue, and how much impact it will have.

"Coronavirus is the black swan of 2020," venture firm Sequoia Capital said in a note last week sent to founders and CEOs of companies it's connected to. Sequoia urged readers to make quick adjustments to their businesses. "A distinctive feature of enduring companies is the way their leaders react to moments like these."