The first person in New York City to undergo testing for the novel coronavirus is being treated in Bellevue Hospital, the city’s health commissioner said Saturday.

The patient, who is under 40, fell ill with a fever, cough and shortness of breath — telltale signs of the illness — after returning from China and going to see a doctor, Health Commissioner Dr. Oxiris Barbot said in a statement.

Testing showed the person didn’t have the flu or a cold virus, so a test for coronavirus was done. The results of the coronavirus test, which is being handled by the federal Centers for Disease Control and Prevention, won’t be known until at least Monday.

The person was not identified, and the city didn’t say where the person lives.

The fact that the person is being tested shows the system the city put in place to handle the outbreak is working, Barbot said.

“This is exactly what we prepared for and we thank everyone for taking all the right steps.”

This is the 12th possible case in New York state. Eight of those tests have come back negative and three are still pending, Gov. Andrew Cuomo’s office said Saturday.

The possible New York City case comes after the eighth US case was identified in Massachusetts late Friday.

The Boston man sought treatment at a hospital shortly after returning from Wuhan, the Chinese city at the epicenter of the outbreak. He had contact with only a few other people before he went to the hospital, Massachusetts officials said.

Other cases in the US are in California, Washington state, Illinois and Arizona.

The death toll in China from the virus, which had not been seen before it appeared in early December, jumped to more than 300 people Saturday, while the number of confirmed cases worldwide soared to 13,800.

All told, 24 countries have reported 134 cases, including a case transmitted person-to-person in Vietnam.

The virus’ rapid spread and concern about the potential for human-to-human transmission outside of China prompted the World Health Organization to declare a global health emergency earlier in the week.

WHO data show the coronavirus has spread far faster than SARS, which infected about 8,100 people in eight months, killing 774, in 2003.

“Countries need to get ready . . . for a domestic outbreak control, if that happens,” said the WHO representative in Beijing, Gauden Galea.

Also on Saturday, scientists at Hong Kong University published research that projects the coronavirus may have infected as many as 75,815 people in Wuhan. The city of 11 million people has been on virtual lockdown for weeks to stem the spread of the disease.

Ominously, the mayor of Huanggang, a neighboring city to Wuhan, predicted a “significant increase” in confirmed cases will be announced Sunday and Monday, according to the Global Times, an English language news outlet published by the Chinese Communist Party’s official People’s Daily.

Between 600,000 and 700,000 people returned to Huanggang from Wuhan before the lockdown, the mayor said.

China is scrambling to build hospitals to handle the surge in cases. Besides the two hospitals under rapid construction in Wuhan — the first is expected to open Monday, the second Wednesday — officials are making quick repairs to a hospital in Beijing originally built to handle SARS, the Global Times said.

At least two other hospitals will soon open in Fuzhou, the capital of east China’s Fujian Province and Harbin in northeast China’s Heilongjiang Province.

Beijing has criticized Washington’s order barring entry to most foreigners who visited China in the past two weeks as “mean,” but Australia took a similar step Saturday. Japan and Singapore have enacted similar measures.

Also Saturday: Several countries, including Britain, South Korea, Singapore and India, evacuated hundreds of citizens out of Wuhan. Britain withdrew staff from its embassy and consulates in China.

Thousands of Hong Kong hospital workers voted to strike starting Monday in an effort to pressure the government to close all borders with China to prevent the coronavirus from spreading.

American Airlines canceled flights to Hong Kong through Monday, a spokeswoman said. Hong Kong flights will be reevaluated twice daily after that. On Friday, the airline cut off flights to mainland China through March 27 after its pilots sued to halt the service citing the unknown health threats from the virus. Earlier, United Airlines and Delta Airlines had suspended all flights to China.

Apple shut down all its official stores on the Chinese mainland from Saturday to Feb. 9.

Beijing’s local authorities asked companies to work from home until Feb. 10 to keep the coronavirus from spreading.

With Post wires