American, United and Delta Airlines each made a remarkable decision Friday: they're suspending almost all air service between the U.S. and China as a result of the coronavirus outbreak.

Specific details:

American will continue service to Hong Kong, but is otherwise suspending China service immediately, through March 27.

United also will continue service to Hong Kong, but will suspend its other routes to China beginning next week, through March 28.

Delta doesn't fly to Hong Kong, but said it will suspend its service to China between February 6 and would not restore it until April 30.

As the day went on, other airlines around the world made similar announcements, from Air New Zealand to Vietnam Airlines. The moves came after some U.S. pilots and flight attendants objected to traveling to China--even suing their own airline and advising their union members not to accept assignments.

Obviously this suspension first affects people who would otherwise be going back and forth to China.

However, it also adds up to a warning for anyone running a business, given concerns that the coronavirus could have a significant impact on the world economy.

"It is a wild card," Richard Clarida, the vice chair of the Federal Reserve, said in an interview Friday with Bloomberg Television. "We're looking into how it translates into the outlook for Chinese growth, for global growth and for how it impacts the U.S."

Amazon, Apple, Facebook, Google, and Microsoft all announced restrictions on their employees traveling to China this week, where even densely populated areas are reportedly "almost empty" as a result of fears of the virus.

However, it was the announcement that U.S. airlines will be suspending travel to China for two to three months that seemed especially significant. As the New York Times summarized:

The travel disruption sent shocks through the stock market and rattled industries that depend on the flow of goods and people between the world's two largest economies. Planning was upended for companies across a vast global supply chain, from Apple to John Deere, the tractor company.

The S&P 500 suffered its worst loss since October, falling 1.8 percent, as the spread of the virus -- and the increasingly urgent efforts by companies and governments to contain it -- fanned fears of an economic slowdown.

There are now about 12,000 cases of the coronavirus worldwide, 259 people have died from it, and health officials say they're concerned that as many as 75,000 people in China may be infected but not yet diagnosed.

Fortunately, there have been only a handful of U.S. cases (and no deaths), but Alex Azar, the secretary of health and human services, called the coronavirus "a public health emergency in the United States."​

Meanwhile, the U.S. Government made several related moves on late Thursday and Friday:

The State Department advised Americans not to travel to China.

The government announced that it will not allow most foreign nationals who have visited China recently to enter the United States, beginning 5 p.m. Sunday, and

The government took the extremely rare step of quarantining 195 Americans who had recently visited Wuhan, China, the locus of the coronavirus outbreak.

On that last point, a Reuters photo appeared to show at least one quarantined child among the Americans who are now confined to March Air Reserve Base for two weeks, in Riverside, California.

Meanwhile, a passenger who tried to leave the base without permission was "intercepted," the New York Times reported.