By and large, the message to the public has been one of reassurance. “We are encouraging New Yorkers to go about their everyday lives and suggest practicing everyday precautions that we do through the flu season,” Dr. Barbot said.

But there is considerable anxiety and debate over the proper precautions within the city’s Chinatowns. That has only grown in the past few days as more alarming news has emerged out of Wuhan about the virus’s spread. So far more than 4,500 people have been sickened and more than 100 people have died.

In response, the authorities in China have imposed a lockdown of some 56 million people in cities in Hubei province, of which Wuhan is the capital, though by the time it was in effect some five million people had already traveled from Wuhan, according to Wuhan’s mayor.

Scott Liu, 56, a textile importer who lives in Queens, said he was on the last direct flight from Wuhan to Kennedy Airport before the flights were canceled last week. He and his fellow passengers learned of the city lockdown mid-flight.

He does not think he is sick, but he knows that symptoms take time to appear — the authorities have said the incubation period is up to two weeks, although symptoms seem to usually appear within a week, Dr. Barbot said.

In the meantime, Mr. Liu has confined himself at home alone, even at the start of Lunar New Year.

Instead of going out to visit friends and family or sharing holiday meals, Mr. Liu stood behind his door as friends dropped off traditional Hubei dishes for Lunar New Year on his doorstep — lotus root and pork rib soup, salted fish and dumplings.

Mr. Liu said he did not think he was overreacting, just acting responsibly.

“For us, this is very serious,” he said in Mandarin during a phone interview on Friday.