A massive power cut has caused disruption across northern India, including in the capital, Delhi.

The outage hit at least six states including Punjab, Haryana, Uttar Pradesh, Himachal Pradesh and Rajasthan early on Monday, officials said.

It is unclear why the network supplying electricity to these states collapsed, but excessive extraction of power by some states could be a reason.

Engineers say it will take some hours to restore power.

The outage happened at 02:30 local time (2100 GMT) on Monday after India's Northern Grid network collapsed.

SK Sonnee, a senior electricity official, told the Press Trust of India news agency that there have been "problems" with the grid, and engineers were trying to restore it.

Thousands of passengers were stranded when Delhi's metro railway services were unable to run in the early hours.

Traffic signals in the capital were not working leading to gridlocks in the morning. Water treatment plants in the city also had to be shut for a few hours.

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