When his restaurant was broken into in early April, Mr. Razavi had already laid off most of his 75 or so employees, and was uncertain whether he would ever reopen. Now, he is out $5,000 from stolen alcohol, a broken door and cleanup costs. “It’s like somebody pouring salt on your wound,” he said.

Although crime rates have fallen across the country, break-ins at small businesses have increased in some cities. The Texas county that contains Houston reported a 19 percent increase in commercial burglaries in late March. There has been a spate of restaurant and bar break-ins in Washington, D.C.

Since New York City declared a state of emergency on March 12, the number of commercial burglaries has surged to 763, from 330 over the same period in 2019, the police said. More than 140 of those break-ins have taken place at restaurants, nearly three times as many as during the same time last year. Other retailers, like gas stations and candy stores, have also seen a big rise in thefts.

“They’re targeting the small merchants, they’re targeting eateries,” said Michael LiPetri, the chief of crime strategies for the New York City Police Department. “It’s outrageous.”

Mr. LiPetri said the department has reassigned detectives from other beats to go after burglars. In San Francisco, the Golden Gate Restaurant Association held conference calls this week in which a crime-prevention nonprofit group taught restaurant owners how to protect their businesses during the pandemic.