The White House advised people who have passed through or left New York City that they should place themselves in a 14-day quarantine.

White House officials expressed growing alarm on Tuesday about the coronavirus outbreak in New York City, advising people who have passed through or left the city to place themselves in a 14-day quarantine.

Officials warned that the outbreak could reach its peak in New York City much sooner than expected and said they had begun treating the region as a coronavirus hot zone, akin to areas of China and Europe overwhelmed by the virus.

About 60 percent of the new cases in the country were in the New York City metropolitan area, and the infection rate was eight to 10 times greater than other parts of the country, officials said at a briefing with the White House Coronavirus Task Force.

“Anyone in the New York metropolitan area who has traveled: Our task force is encouraging you to monitor your temperature, be sensitive to symptoms, and we are asking anyone who has traveled out of the New York City metropolitan area to anywhere else in the country to self-isolate for 14 days,” Vice President Mike Pence said.

“We have to deal with the New York City metropolitan area as a high-risk area,” he added.

Dr. Deborah L. Birx, the White House’s coronavirus response coordinator, and Dr. Anthony Fauci, the director of the National Institute of Allergy and Infectious Diseases, said they were very concerned about people from New York City spreading the virus.

“We are starting to see new cases across Long Island that suggest people have left the city,” Dr. Birx said. “We can have a huge impact if we unite together.”

It was not clear if the White House had alerted Gov. Andrew M. Cuomo about the quarantine. “We’re talking to them about it,” President Trump said.

The White House warning came as Governor Cuomo offered a grim forecast for the outbreak in New York, saying that it would flood the state’s strained hospitals with as many as 140,000 stricken patients in the next few weeks.

Mr. Cuomo said that in New York City, new cases appeared to be doubling every three days. The crisis has already claimed the lives of more than 200 people statewide.