“We find ourselves with little to no empirical evidence of what’s happening,” said Mr. Miller, because the virus outbreak became a factor so late in March. “I don’t have a sense, other than it’s going to be catastrophic.”

Contracts and closings can lag the reality of the market by several weeks or months as paperwork makes its way through the system, but there are already some signals of decline.

At the end of March, there were 5,801 active listings for sale in Manhattan, down 15.3 percent from the same period last year, said Noah Rosenblatt, the chief executive and founder of UrbanDigs, a real estate data company. And 1,159 listings were taken off the market, compared with just 417 the same time last year.

One of the biggest obstacles for the real estate market will be trying to sell apartments under virtual lockdown. Real estate agents in New York had been deemed nonessential workers, so in-person showings were effectively banned, although new guidance from the Cuomo will now allow showings and some back-office real estate functions to continue. And few apartment buildings are allowing visitors or move-ins. Even if buyers agree to purchase a home sight unseen, many of the steps toward closing remain stubbornly analog, in spite of efforts to incorporate video calls and other technology into the process.

Before the pandemic, “2020 would have been a very strong recovery year for us,” said Diane Ramirez, the chief executive of Halstead, a real estate brokerage firm. “I can’t even begin to think of what it will be like now.”

The luxury market, which is in a yearslong price correction, could be further affected. Last week, only two properties in Manhattan went into contract at $4 million or more, the lowest weekly sales rate since August 2009, during the last recession, said Donna Olshan, the president of Olshan Realty. In the last week of March 2019, 21 contracts at or above that price were signed.

“Anything left on the market now, the price is just a suggestion,” she said, noting that sellers already in contract, as well as new buyers, are pushing for more aggressive price cuts.