New Jersey Transit, which operates a vast network of commuter trains and buses, has seen a roughly 20 percent decline in bus and rail ridership this week compared to the same days last week, according to preliminary data from agency officials. Ridership on the PATH rail network, which links cities in northern New Jersey to Manhattan, also declined nearly 20 percent in the first three days of this week compared to last week, according to Port Authority officials.

“I think that we’re going to see an uptick in ridership falling off a little bit and that’s to be expected,’’ Sarah Feinberg, the interim president of New York City Transit, which operates the subway and buses, said Thursday on the Brian Lehrer radio show. “I mean, I think we have not seen the worst of this virus yet.”

Officials expect even steeper ridership declines in the coming weeks now that the state and city have imposed sweeping restrictions on large gatherings, forcing the closing of Broadway theaters and many museums. An increasing number of employers are telling their employees to work from home.

So far transit officials have not considered reducing service, but may decide to do so if ridership drops dramatically or health officials advise it, Ms. Feinberg said.

N.J. Transit riders who purchased monthly passes but are now working from home can mail in their passes and receive a prorated refund, according to the New Jersey Transit website. An M.T.A. spokeswoman said that a refund policy for riders who have purchased monthly MetroCards will be reviewed.

A similar decline in ridership has taken place in public transit systems in other cities where confirmed cases of coronavirus are ballooning. Last week, on San Francisco’s BART commuter rail, ridership slipped by 8 percent from the previous week. On Monday, ridership dropped 25 percent compared with the previous Monday.