Delta Air Lines on Friday suspended all flights from the United States to China through April as major U.S. carriers took a dramatic step to severely limit travel between the two nations amid a virus outbreak.

Within hours, American and United airlines followed suit, joining dozens of airlines around the world that have reduced or suspended service to mainland China over concerns about coronavirus. All flights to the U.S. from China in coming days will go to one of seven major airports where passengers can be screened for illness, the U.S. government said Friday.

The moves came a day after the U.S. State Department advised Americans not to travel to China and, if there, to leave as soon as possible. The easily transmitted illness, which originated in Wuhan, China, has sickened nearly 11,000 people worldwide and killed about 250. British Airways, Finnair, Air France and others also restricted flights to and from China.

Passengers who must reach China can still book flights to airports in the surrounding region, such as Hong Kong, where several Asia-based airlines continue to offer flights in and out of the mainland. American Airlines will continue flights to Hong Kong from Los Angeles and Dallas while United will operate a once-daily flight between San Francisco and Hong Kong. Delta does not fly nonstop to that city.

Delta, the dominant carrier at Minneapolis-St. Paul International Airport, will suspend all U.S. to China flying starting Feb. 6 and lasting through April 30. Balancing customers' desire to get out of China and crew members' anxieties, Delta will continue to operate flights until Feb. 5 to ensure customers looking to leave China can do so.

"Going from a reduction of service to an all-out suspension was really with our employees in mind," Delta spokesman Michael Thomas said. "We wanted to protect employees while helping our customers get out."

China represents a small but important part of Atlanta-based Delta's flight operations, accounting for just 2% of its passenger revenue.

Thirty minutes after Delta's announcement, Dallas-based American Airlines suspended flights to China through March 27, followed a few hours later by United's decision to suspend its mainland China flights beginning Feb. 6 through March 28. Chicago-based United has the largest Asia network of the three major U.S. carriers.

Nearly 10,000 flights were suspended between Jan. 23 and Jan. 28, according to aviation analytics firm Cirium.

"While the industry is playing its part to help prevent the spread of the virus, the outbreak will inevitably cause significant disruption of schedules and travel patterns in the short and medium term," Cirium chief economist Peter Morris, said in a statement.

Delta's last flight to China before the suspension will leave the United States on Monday. Its last flight from China will be Feb. 5.

Delta currently operates 42 flights a week between the U.S. and China. Travelers with flights already booked can request a refund or reschedule their trips for after April 30. Delta's China flight suspension lasts a month longer than its major U.S. competitors to avoid later extensions.

"If the conditions warrant, or things change, we can reassess the restart of our operations in China," Thomas said, "whether that is moving them forward or pulling them back beyond the date we currently have set."

Delta operates nonstop flights to Beijing and Shanghai from a handful of its U.S. hubs, including Detroit, Seattle, Atlanta and Los Angeles. More than a year ago, the airline petitioned the U.S. government to grant it an unused route slot for daily nonstop flight between Minneapolis-St. Paul and Shanghai. The Department of Transportation has not yet made a decision on that request.

Many Delta passengers connect to Chinese cities beyond Beijing and Shanghai through its partnership with China Eastern, a Shanghai-based airline in which Delta holds a small ownership stake.

China Eastern has taken the biggest hit so far from the coronavirus outbreak, according to data released Friday by Cirium. It did not operate 1,591 flights between Jan. 23 and Jan. 28.

Several U.S. pilot and flight-attendant groups and unions expressed concern in recent days about the risk to their members flying to and from China.

"For the flights we do have over the next few days, we've been in touch with our crew members flying on those routes and making sure those aircraft are provisioned with gloves and masks, and a number of mitigation plans are in place to make sure they are well taken care of at hotels and otherwise during their layovers," Thomas said.

The Dow Jones industrials average dropped more than 600 points Friday as investors' concerns rose about the effect a crippled Chinese economy could have on the rest of the world.

Economists are looking to past health crises, like the 2003 SARS outbreak that hit Hong Kong the hardest, for what the coronavirus could mean. The epicenter for this outbreak, Wuhan, is interior China with less direct access to outside countries, leading some to surmise the virus' spread could be slower.

But a report from S&P Global Markets noted, "China's air travel market is larger and better connected to the rest of the world than ever before, both in absolute terms and as a percentage of global aviation (Chinese airlines carry 15% of global air traffic). Hence, larger ripple effects are likely if the coronavirus continues. China's economy will face at least a temporary hit, which will affect a variety of sectors including most notably transportation, tourism, and retail."