Hours earlier, Gov. Andrew M. Cuomo of New York compared a jump in cases on Long Island to “a fire spreading,” and said that “New Jersey has a serious problem.”

Though New York City remains the nation’s epicenter for the coronavirus outbreak with thousands of new cases every day, officials are increasingly concerned about emerging hot spots near the city.

Citing coastal communities increasingly crowded by those fleeing other hot spots, Mr. Murphy announced that New Jersey would move to make it easier for municipalities or counties to block “rentals to transient guests or seasonal tenants” for the duration of the crisis, including at hotels and motels.

On Long Island, a rapid increase in cases brought New York City’s share of the statewide cases down to 65 percent, from 75 percent. It raised questions about the continuing migration of the city’s residents to second homes in beach communities or areas of the Hudson Valley — though Mr. Cuomo said he did not know if that kind of movement was contributing to the increase in cases on Long Island.