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 . Read about a train fire in India that kills 32 . 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 .
Outage held up at least 300 trains in the region , Indian railway spokesman says . Comment: Power was partially restored after about six hours , authorities said . Blackouts become more common during summer every year when demand shoots up .