“My wife said we could get a Mustang, but I wasn’t going to go out shopping for a car,” Mr. Maletic said.

The drop in sales is the second big blow to automakers. Most companies have shut down factories across North America to prevent the spread of the virus among workers.

Automakers and dealers expect a bigger decline in April because stay-at-home orders will be in effect for most or all of the month in many parts of the country. Even as some states lift or relax those orders, consumers will likely stay away from showrooms for some time. To lure buyers, G.M., Ford Motor and Fiat Chrysler are offering zero-percent loans that last up to seven years for new car purchases.

In St. Louis, where a lockdown order has been issued by the local government, Ann Kittlaus is unsure of how to trade in her family’s 2017 Acura MDX, since the lease is expiring soon. “We would have to have the dealer deliver a new one and take the other away,” said Ms. Kittlaus, a public relations professional and mother of two college-age children.

She added she would probably let the vehicle sit for a week to be sure it doesn’t have any traces of the virus. In any case, she said she is not in a hurry to make the trade. “It’s not like we’re going anywhere,” Ms. Kittlaus said.

A dramatic drop in sales in April could cause a painful chain reaction. With no buyers driving cars off their lots, dealers won’t have to order more from the manufacturers. That could force car companies and their suppliers to keep their plants idle or production low even once officials allow more people to go back to work.

“April is likely to see further historic declines, driven largely by a lack of consumer confidence and substantial increases in unemployment,” said Charles Chesbrough, a senior economist at Cox Automotive. “And that trend will likely continue into early summer, at best. The second quarter will be the real measure of Covid-19’s impact on the economy and the auto industry.”