A message popped up on Sgt. Joseph Rosso’s phone. It was not a robbery in progress, or a report of shooting, or a domestic dispute. The message said a small crowd had gathered outside a Trader Joe’s grocery store in Lower Manhattan.

Ordinarily, a cluster of people in front of a city store would not merit the police’s attention. But these are not ordinary times. Shaking his head, Sergeant Rosso stepped on the gas, and the police cruiser lurched forward, its red and blue lights blaring. As the car neared 14th Street and Second Avenue, about 10 people in front of the grocery store slowly stepped apart.

“I’ve lived in the city my whole life, I’ve never imagined this,” Sergeant Rosso said. “It’s very surreal.”

This is law enforcement in the age of a pandemic. Sergeant Rosso and his partner, Officer Nicholas Contardo, are members of a 708-member task force that has been drawn from other duties to enforce social-distancing rules intended to stem the spread of the coronavirus.