NEW DELHI — A power grid failure blacked out northern India for hours Monday, halting trains, forcing hospitals and airports onto backup power and providing a dark, sweltering reminder of the nation’s inability to meet its energy needs as it strives to be an economic power.

While the midsummer outage was unique in its reach — it hit 370 million people, more than the population of the United States and Canada combined — its impact was softened by Indians’ familiarity with almost daily blackouts of varying duration. Hospitals and major businesses have backup generators that seamlessly kick in during power cuts, and upscale homes are hooked to backup systems powered by truck batteries.

Nonetheless, some small businesses were forced to shut for the day. Buildings were without water because the pumps weren’t working, and the vaunted New Delhi Metro, with 1.8 million daily riders, was paralyzed during the morning commute.

“This will obviously get worse,” said Subhash Chawla, a 65-year-old retiree who took the Metro once power was restored. “Unless the Metro has a separate power supply, it will be chaos in the future.”

The grid that failed feeds the nation’s breadbasket in Punjab, the war-wracked region of Kashmir, the burgeoning capital of New Delhi, the Dalai Lama’s Himalayan headquarters in Dharmsala, and the world’s most populous state, poverty-stricken Uttar Pradesh.

Most affected areas had power back by late morning, less than nine hours after the outage started. By evening, 15 hours after the outage began, officials said full power had been restored.

Many chafed at the inconvenience.

Amit Naik, a toy maker in New Delhi, was forced to close his workshop for the day.

“There was no water, so my machine couldn’t run. Other people had the same difficulties,” he said.

The Confederation of Indian Industry said the outage was a reminder of the urgent need for the government to fix the power sector, ensure a steady supply of coal for power plants and reform the electricity utilities.

Transmission and distribution losses in some states are as much as 50 percent because of theft and corruption by employees in the power industry. India’s Central Electricity Authority reported power deficits of about 8 percent in recent months.

Power Minister Sushil Kumar Shinde deflected criticism, pointing out that the United States and Brazil also had huge power failures in recent years.

“I ask you to look at the power situation in other countries as well,” he said.

The blackout, the worst to hit India in a decade, began about 2:30 a.m. when the grid covering eight northern states crashed. Officials in Uttar Pradesh, where the problem was believed to have begun, said the grid could not keep up with the huge demand for power in the hot summer.

But Shinde said he was not sure exactly what caused the collapse and had formed a committee to investigate.

The outage left millions sweltering in the summer heat. Muslim families were forced to eat their pre-dawn meals by candlelight before beginning their daytime Ramadan fast. “It was really difficult,” said farmer Mohammed Zaman.

As officials struggled to get the grid back on line, they drew power from the neighboring eastern and western grids as well as hydroelectric power from the small neighboring mountain kingdom of Bhutan.

New Delhi residents were roused from sleep when their fans and air conditioners stopped, and came out of their homes in the heat as the entire city turned dark. Temperatures in the city were in the mid-30s C (90s F) with 89 percent humidity.

Some trains across the northern region were stranded when their electric engines failed. Others were delayed by hours as they were hooked to diesel engines.

The failure was the first time since 2001 that the northern grid had collapsed. But India’s demand for electricity has soared since then as its population and economy have grown sharply.

But any connection to the grid remains a luxury for many. One-third of India’s households do not even have electricity to power a light bulb, according to last year’s census.

The power deficit was worsened by a weak monsoon that lowered hydroelectric generation and kept temperatures higher, further increasing electricity usage as people seek to cool off. Shivpal Singh Yadav, the power minister in Uttar Pradesh, home to 200 million people, said that while demand during peak hours hits 11,000 megawatts, the state can only provide 9,000 megawatts.

Uttar Pradesh Power Corp. chief Avnish Awasthi blamed the grid collapse on states drawing more than their allotted power to meet the summer demand.

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Associated Press writer Biswajeet Banerjee in Lucknow and Aijaz Hussain in Srinagar contributed to this report.