The electricity supply to India's capital Delhi has been largely restored after a two-day blackout, but much of the country remains without power.
More than 600 million people have been affected in India after three power grids collapsed, one for a second consecutive day.
The breakdowns in the northern, eastern, and north-eastern grids affected at least 20 of India's 28 states.
Transport networks ground to a halt with hundreds of trains stranded and water supplies interrupted.
In eastern India, about 200 miners were trapped underground as lifts failed, but officials later said they had all been rescued.
Full power is not expected to resume until sometime on Wednesday.
In Delhi, Metro services were halted and staff evacuated trains, the BBC says.
Many traffic lights in the city failed, leading to massive traffic jams.
Streets in Calcutta were plunged into darkness as night fell.
Other areas affected included Delhi, Punjab, Haryana, Uttar Pradesh, Himachal Pradesh and Rajasthan in the north, and West Bengal, Bihar, Orissa and Jharkhand in the east.