On a day that over 600 million people were grappling with the electricity crises, the government moved Sushil Kumar Shinde from the power ministry to the more sensitive home ministry.

The power failure also left around 200 miners trapped in a mine in West Bengal's Burdwan district. The miners of Eastern Coalfields Ltd (ECL) were rescued after emergency power supply was arranged.

Over 300 trains were also left stranded mid journey for hours, affecting around 300,000 rail passengers.

The power was restored to a large extent at around 7.30 p.m. after more than six hours. Monday's blackout had lasted from 2.30 a.m. to late morning.

"The grid incident occurred at 1 p.m., affecting the northern, eastern and northeastern grids. The system is under restoration," said the official website of the Eastern Grid, among the systems managed by the state-run Power System Operation Corp Ltd.

The states affected Tuesday were Jammu and Kashmir, Himachal Pradesh, Punjab, Haryana, Delhi, Rajasthan, Uttar Pradesh, Bihar, West Bengal, Odisha, Jharkhand, Sikkim, Assam, Meghalaya, Tripura, Nagaland, Manipur, Mizoram and Arunachal Pradesh.

These states account for half of India's 1.2 billion population.

"Oh, not again. We faced a terrible situation yesterday. What is the government doing, were no lessons learnt from yesterday's blackout," said an exasperated Paloma Guha, a new mother trying to make her baby sleep in the heat.

Shinde, who had constituted a committee to probe the failure Monday, attributed the collapse to overdrawing of power by four states - Uttar Pradesh, Punjab, Rajasthan and Haryana. However, all four states denied the charge.

The capital's popular Delhi Metro, which caters to 1.8 million passengers on a week day, suspended service on all its six lines due to the power trip, inconveniencing thousands of passengers. Metro services were resumed fully at 5.30 p.m.

There was chaos on the streets of the national capital as Delhi Metro commuters spilled on to the streets to look for alternative transport. With traffic-lights on the blink, over 4,000 traffic policemen manned the intersections amid the intermittent rain.

Hospitals in Delhi were unaffected by the crises due to their power back-ups, as was Delhi's international airport. Flight operations remained normal.

Speaking to reporters here at around 4 p.m., chairman and managing director of state-run Power Grid Corp of India R.N. Nayak, said the failure was due to overdrawal of power by some states and that a full inquiry would reveal the nature of the problem. He added that every effort was being made restore supplies fully by 7-7.30 p.m, but normalcy would return only by midnight.

He said the excess power drawn by the states had a cascading effect on the other states.

The Power Grid Corporation of India, which controls the country's transmission network, said that situation across the country is expected to be normal by midnight.

"We are trying to restore (power to normalcy) all over the country by midnight," Nayak said.

At present, the Northern Grid is getting power from Gwalior and Agra substations as well as from three hydel projects - Tehri and Vishnu Prayag in Uttarakhand and Nathpa Jhakri plant in Himachal Pradesh - he said.

According to Nayak, the demand across the three regions is around 55,000 MW.

Except for few areas in Kolkata and Delhi, and Narora (Uttar Pradesh), all three regions were affected, he said.

At the time of failure, Northern Grid's demand was about 32,400 MW, Eastern Grid (12,000 MW) and North Eastern Grid (1,100 MW), respectively.

Bihar Chief Minister Nitish Kumar said the central government should ensure that no state draws electricity beyond its sanctioned load. "For this, they will have to develop and strengthen the infrastructure".

The US had faced a major power blackout in early July following a storm, that left large parts of the the East Coast without power for a few days and affected two million people.