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Chinese officials warned Sunday that the deadly new coronavirus is likely to spread as the United States prepared to evacuate diplomatic officials stationed in the city of Wuhan, where it's believed to have originated.

Ma Xiaowei, minister of China's National Health Commission, or NHC, said at a news conference that the incubation period for the coronavirus — the period between exposure and the appearance of first symptoms — can range from one to 14 days and that it is infectious during this time.

That was not the case with Severe Acute Respiratory Syndrome, or SARS, which killed nearly 800 people during the 2002-03 epidemic, which also originated in China, he said.

"At present, the rate of development of the epidemic is accelerating," Ma said. "I am afraid that it will continue for some time, and the number of cases may increase."

*Main developments with #China virus: health officials say strength & pace of virus getting stronger; admit ‘pressure’ on prevention controls with epidemic entering complicated stage; shortage of medical supplies esp protective suits; confirmed 3rd US case in California. @NBCNews — Janis Mackey Frayer (@janisfrayer) January 26, 2020

In a separate statement, the NHC confirmed that 56 people had died from the virus and that almost 2,000 others had been infected. There are more than 2,600 suspected cases, it added.

The coronavirus, which spreads through respiratory transmission, belongs to the same family as the strain that caused SARS. Not much is known about how the virus causes an infection, but it can lead to symptoms like fever, coughing, wheezing and pneumonia.

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While the virus may have evolved from wild animals to humans in the early days, Ma said, it is now gradually adapting to survive in humans and entering the period of human-to-human transmission.

"From now on, the spread of the epidemic is relatively fast, which brings some challenges and pressures to prevention and control," he said. "Experts predict that the epidemic is now entering a more severe and complicated period."

Ma added that there was no evidence to suggest that the virus has mutated but said the possibility of the virus's changing over time may not be ruled out.

Meanwhile, the U.S. State Department announced plans Sunday to evacuate its personnel stationed in Wuhan.

The State Department said it will also book a limited number of private U.S. citizens onto the flight, which is scheduled to depart Tuesday. It said priority would be given to Americans at greater risk from coronavirus.

Other countries, including France and Australia, have also said they are considering options to get their citizens out of Wuhan.

Japan announced plans Sunday to arrange for a charter plane for Japanese nationals in Wuhan. Japan has now recorded its fourth confirmed case of the virus.

Meanwhile, three more people were confirmed as coronavirus patients in the United States on Sunday: one in Orange County, California; one in Los Angeles County, California; and one in Maricopa County, Arizona. Two previously confirmed cases involve patients in Washington state and Chicago.

The disease has now spread to four continents, as Australia announced three confirmed cases in Sydney on Saturday. Canada also declared its first "presumptive" confirmed case Saturday.

A sixth case was confirmed in Hong Kong on Sunday, a day after the city's chief executive declared the highest level of emergency.

Authorities in the region halted ticket sales for trains going to Wuhan last week. They also suspended flights from Wuhan into Hong Kong. Two of Hong Kong's major tourist attractions, the Hong Kong Disneyland and Ocean Park theme parks, were closed Sunday.

Officials at the World Health Organization said last week that the outbreak has not yet reached a level that would classify it as a global public health emergency.

But the epidemic has left more than a dozen cities in China on lockdown, including Wuhan, where the virus is believed to have originated at a seafood market late last year, forcing millions of people to cancel their travel plans amid the traditionally busy Lunar New Year celebrations.

China announced a nationwide ban on wildlife trade in markets and e-commerce platforms Sunday until the epidemic is under control. President Xi Jinping said during a politburo meeting Saturday that China was facing a "grave situation."