New Delhi (CNN) -- A grid failure cut power supplies in northern India on Monday, hitting rail and road transport for hours in the country's worst blackout in a decade, authorities said.
The outage held up at least 300 trains in the region, Indian railway spokesman Anil Kumar Saxena told CNN.
India's Power System Corporation Limited reported the collapse at 2.35 a.m. local time. Officials say it affected seven states in northern India, home to more than 350 million people.
Residents spent overnight drenched in sweat amid humid weather, and many backup power systems had run out by daybreak. Power was partially restored after about six hours, authorities said.
"When the northern grid failed, we started taking power from eastern and western grids," Indian Power Minister Sushilkumar Shinde told reporters. "We will take some power from Bhutan, too," he said.
The blackout left passengers stranded at train stations, and signal failures caused traffic snarls that choked the Indian capital's already congested roads during office hours.
Indians, however, have been no stranger to power cuts, which become more common during summer every year when demand shoots up.
But Shinde, who ordered an investigation into Monday's outage, said the last time that an entire grid failed in north India was 10 years ago.
Although it's Asia's third-largest economy, India still heavily depends on coal for its expanding energy needs. Of the nation's total installed capacity of 205,340 megawatts, less than 3% comes from nuclear sources, data posted on the power ministry's website show.
And according to figures from the Central Electricity Authority, the nation suffered a supply shortfall of 8.6% in June.
In a statement, the country's top business lobby, the Confederation of Indian Industry, called for immediate reforms in the power sector.
"The increasing gap between the demand and supply of electricity has been a matter for concern," it said as it urged boosting coal availability to the country's power plants. "Today's outage is an urgent reminder for addressing these issues as a priority," it added.