India’s worst blackout in more than a decade left at least 300 million people in New Delhi and northern parts of the country without power for eight hours or more on Monday, with the failure of an overloaded grid providing a sobering reminder of the nation’s struggle to meet its energy needs as it bids to become an economic powerhouse.

Trains were stopped in their tracks as power went out in the early hours Monday in Delhi and seven northern states. The much-vaunted New Delhi Metro was badly hit during the morning commute, and the failure of traffic lights above ground caused gridlock on the streets.

Hospitals, airports and major industries are used to power shortages here and many moved seamlessly onto backup diesel generators, but many small businesses were forced to close, and buildings were left without water as pumps shut down.

Indian industry leaders blamed the incident on a large and growing gap between electricity demand and supply, something that the government has failed to tackle despite repeated pledges to do so. Some senior government officials say reform of the power sector is the greatest challenge facing Asia’s third-largest economy in the next few years.

“One of the major reasons for the collapse of the power grid is the major gap between demand and supply,” said Rajiv Kumar, secretary general of the Federation of Indian Chambers of Commerce and Industry. “There is an urgent need to reform the power sector and bring about infrastructural improvements to meet the new challenges of the growing economy.”

India suffers a power deficit in peak periods of 8 percent to 12 percent, and power cuts of eight hours a day are common in many parts of the country.

Middle-class residents of New Delhi complained of waking up drenched in sweat as fans and air conditioners failed, but others would not have noticed the difference — about 300 million Indians, or a quarter of the population, have no access to electricity at all.

India has the world’s fifth-largest reserves of coal, but the country’s wrangles over environmental and land clearances, as well as its failure to invest in mines and technology, have prevented output from growing and keeping up with demand.

Losses in electricity transmission and distribution are also among the world’s highest, 24 percent to 40 percent, because of inefficiencies and theft.

Power Minister Sushilkumar Shinde said India has one of the world’s best power grids and pointed out that the United States and Brazil also suffered big power failures in recent years.