A U.S. Navy ship outfitted with 1,000 hospital beds pulled into New York Harbor. Tents sprung up in New York City’s Central Park. The Javits Center, a 1.8 million-square-foot convention center in Manhattan, opened its doors as a makeshift hospital.

They are part of a striking new reality in New York City and across America, as state and federal leaders take steps unprecedented in modern times to fight the global coronavirus pandemic that has infected nearly 160,000 Americans and more than 775,000 people globally.

With...