A massive power breakdown has hit northern and eastern India for a second day running, leaving more than half the country without power.
Officials said there was a total blackout in Delhi. All Metro services had been halted and staff were trying to evacuate trains.
Power ministry officials said the eastern grid had also collapsed.
A massive power failure caused severe disruption and travel chaos across northern India on Monday.
It was unclear why the supply collapsed on Monday but reports said some states might have been using more power than authorised.
Power officials had managed to restore the northern grid by Monday evening, but at 01:05pm (0735 GMT) on Tuesday, the grid collapsed again.
The eastern grid failed around the same time, officials said.
"Both the northern and eastern grids have collapsed. Please allow us to address the problem," AFP quoted VK Agrawal, the general manager of the northern grid, as saying.
The two grids together serve more than half of India's 1.2bn people.
The breakdown has hit a large swathe of the country including Delhi, Punjab, Haryana, Uttar Pradesh, Himachal Pradesh and Rajasthan states in the north and West Bengal, Bihar, Orissa and Jharkhand in the east.
An official in Orissa said the blackout in the eastern grid had been triggered by a fault and could take several hours to resolve.
Correspondents say India faces a chronic power deficit and unless there is a huge investment in the power sector, the country will see many more dark days ahead.