NEW DELHI — Northern India’s power grid crashed today, halting hundreds of trains, forcing hospitals and airports to use backup generators and leaving 370 million people — more than the population of the United States and Canada combined — sweltering in the summer heat.

The blackout is the worst to hit India in a decade.

Some small businesses were forced to shut for the day. Buildings were without water because the pumps weren’t working.

The northern grid crashed about 2:30 a.m. because it could no longer keep up with the huge demand for power in the hot summer, officials said.