Officials were assessing the cause of the problem on the Northern Power Grid and the number of people hit, but reports pointed to a fault in one state that led to an auto-shutdown in surrounding areas.

The Press Trust of India said the area around the capital New Delhi, as well as the states of Punjab, Haryana, Uttar Pradesh, Himachal Pradesh and Rajasthan had all been affected when supplies dropped out in the early hours of Monday.

Trains and metro services as well as hospitals had been hit, officials said.