Hospitals in U.S. pandemic epicenters have passed a tipping point in the fight against the new coronavirus as the relentless climb in infections forces some to move patients to outlying facilities, divert ambulances and store bodies in a refrigerated truck.

New York, home to the nation’s largest outbreak of Covid-19, the illness caused by the new coronavirus, is rushing to build a temporary hospital in a Manhattan conference center in the hope of staying ahead of the fast-spreading disease.

Hospitals...