Open this photo in gallery Air China employees wear medical masks for protection against the novel coronavirus outbreak at LAX Tom Bradley International Terminal on February 2, 2020 in Los Angeles. David McNew/Getty Images

United Airlines said late on Wednesday it will extend cancellations of all U.S. flights to China through late April due to the coronavirus epidemic.

With the announcement by Chicago-based United, all U.S. passenger carriers flying to China have now cancelled flights into late April. Carriers say part of the reason is a dramatic drop-off in demand.

United said it was extending cancellations of flights to Hong Kong, which had been set to resume on Feb. 21, and for flights to mainland China, that had been set to resume on March 28. Flights will resume starting April 24.

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United normally operates roughly 12 flights per day from the United States to mainland China and Hong Kong.

American Airlines Group Inc, the largest U.S. carrier, said on Tuesday it was extending the suspension of its China and Hong Kong flights through April 24, amid reduced demand due to the coronavirus outbreak. The carrier had earlier suspended its China and Hong Kong flights until March 27.

The U.S. government has placed new restrictions on travellers to the United States who have visited China, barring nearly all non-U.S. residents if they have been in China within the last 14 days.

The United States is also limiting flights from China or other international flights with U.S. passengers that have been to China within the previous 14 days to 11 major U.S. airports for enhanced screening. It requires a quarantine of U.S. citizens who have recently visited Hubei province in China.

Delta Air Lines Inc previously suspended flights to China through April 30.

The outbreak is disrupting international travel demand.

On Wednesday, the Mobile World Congress, an annual telecoms industry gathering that draws more than 100,000 visitors to Barcelona, was cancelled after a mass exodus by exhibitors due to coronavirus-related concerns.