In the worst ever power crisis, over half of the country's population in 21 states went without electricity for several hours on Tuesday as three majortransmission grids failed, bringing northern, eastern and northeastern regions to a grinding halt.

The massive failure came less than 24 hours after the Northern Grid collapsed and was revived on Monday.

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On Tuesday, the worst sufferers were 265 miners who got trapped in coal mines in West Bengal and Jharkhand due to power outage. They were evacuated after hours of agony.

In the national capital, thousands of Metro commuters had a harrowing time when the trains stopped inside the tunnels as transmission lines tripped at 1 pm. Railway services too were hit, with 300 trains getting disrupted in seven zones in 10 states.

In the national capital, the power collapse triggered disruption in Metro and train services, crippled water supply and choked roads due to non-functional traffic lights.

For the first time, the three inter-state transmission networks -- Northern Grid, Eastern Grid and North-Eastern Grid -- tripped together. While no official reason was given for the failure, sources said the trouble started in the eastern grid.

In its latest update at 8.30 pm, the Power Grid said the northeastern region has been completely restored. While electricity has been fully restored in Delhi, 70 per cent normalcy has been achieved in the northern region so far. However, half of eastern India still remains in dark."Power supply has been extended to all the affected states," it said.

The grid failure and the chaos followed on a day when, in a Cabinet reshuffle, Power Minister Sushilkumar Shinde was moved to the home ministry and Corporate Affairs Minister Veerappa Moily was given the additional charge of power.

The states affected included Delhi, Uttar Pradesh, Punjab, Haryana, Himachal Pradesh, Jammu and Kashmir, West Bengal, Chhattisgarh, Bihar, Jharkhand, Odisha, Sikkim and Assam. Besides 21 states, Union Territory of Chandigarh was also affected.

Shinde said some states were overdrawing power."I was told (by officials) that about 3,000 MW extra power has been over drawn from the Eastern Grid. We have given the direction to either stop it (overdrawal) or we will take action against them," he said.

The Punjab government denied the state's overdrawal from the Northern Grid. It said the state's overdrawal was a meagre 1.2 per cent of its sanctioned load when the grid collapsed, while Haryana's overdrawal was a whopping 22.4 per cent and that of Uttar Pradesh was 6.4 per cent.

The UP government said taking into consideration the parameters at the time of grid failure there was no reason to believe power operations by the state triggered the grid collapse. The denials came after Delhi accused UP, Haryana and Punjab of overdrawing power from the Northern Grid.

Meanwhile, Gujarat Chief Minister Narendra Modi and Bihar Chief Minister Nitish Kumar said the Centre should evolve a system to ensure that no state received more than their quota of electricity for them.