New York state saw a surge in new coronavirus cases Thursday after 22 people were diagnosed with the virus and at least 1,000 people were self-quarantined in suburban Westchester County, just north of New York City.

The number of cases in the state doubled overnight following an increase in testing, according to New York Governor Andrew Cuomo. "The number will continue to go up," he told a news conference. "The more you test, the higher number you will have."

Two new cases — involving a man in his 40s and a woman in her 80s — were confirmed Thursday. Both patients have been hospitalized in intensive care.

Neither of the patients traveled to an infected area or had contact with others known to have COVID-19, meaning their infections could be from "community spread," the cause of which is unknown.

One other case of community spread has been diagnosed in a lawyer in his 50s who is in critical condition at New York-Presbyterian/Columbia University Irving Medical Center.

Dr Howard Zucker, commissioner of the state Health Department, said the patient is believed to have a host of underlying medical issues, mainly respiratory, which made his immune system susceptible to the virus.

The man commuted daily to his office in midtown Manhattan. After catching the virus, he infected his wife, 20-year-old son, 14-year-old daughter and a neighbor who drove him to the hospital.

His family members, his neighbor and the neighbor's friends are now isolated at home.

The synagogue that he attended will halt services this weekend. More than 1,000 people connected to that house of worship are self-isolating after attending a recent bat mitzvah and a funeral.

New York officials said they have enough kits from the Centers for Disease Control and Prevention (CDC) to carry out 1,000 tests.

But on Wednesday, the city said face masks were in short supply.

New York City is home to 8.6 million people. It has the largest subway system in the world with 472 stations that operate around the clock.

At least 5.6 million people take the subway daily on weekdays, according to figures from the Metropolitan Transportation Authority (MTA).

Amid fears about using the city's public transportation system during the outbreak, the city's MTA this week began a widespread campaign of disinfecting buses, subways and trains that go to and from the city's suburbs.

Commonly touched surfaces, including turnstiles, ticket and vending machines, and handrails will be disinfected daily. authorities said.

Disinfecting will be carried out every 72 hours at all 472 subway stations, and a daily deep clean will be done on the city's 6,714 subway cars, 5,700 buses as well as cars on railroads on suburban routes.

Oxiris Barbot, the city's health commissioner, said that there was "no indication" that "casual contact", such as getting on the subway with someone who is sick, is "going to increase the risk to everyday New Yorkers".

Amid the spread of coronavirus, the MTA is running announcements on subway stations, buses and rail cars.

The city's taxi commission has instructed drivers and owners to disinfect their cars at least once a day.

Organizers of the New York International Auto Show, which runs from April 10-19, said it will take place as scheduled. The show, held at the Jacob Javits Convention Center in Manhattan, will have at least 70 hand-sanitizing stations throughout the exhibition floor. A team of specially trained paramedics will be on site.