Senior Power Grid Corporation officials attributed the breakdown to fog combined with pollution in Delhi, Haryana and western Uttar Pradesh. Deposit of pollution particles on transmission lines was attributed as the reason for tripping, which officials described as a common phenomenon during winter - which has been unusually long this year.

"Normalcy was restored at around 1030 hrs," S K Soonee, Executive Director (System Operation) of Power Grid Corporation of India Ltd (PGCIL), said.

"Fog combined with pollution gets deposited on insulators and causes a flash over. This has been happening for quite some time. However, the situation is getting aggravated now.

We are trying to find a permanent solution to the problem," he said.

Delhi, Uttar Pradesh and Haryana were the most hit due to the failure in the lines.

Train movement was badly affected in the region due to the power failure, with the worst affected sections being Ferozabad-Dadri and Tughlakabad-Palwal lines, where electricity supply was disrupted since 0345 hrs and 0615 hrs respectively.

The power failure, however, was first reported at midnight, officials said.

A senior Railway official said diesel locomotives had been dispatched to resume the services.

A passenger on the Gwalior-bound Shatabdi Express said: "There is no train movement since the last two hours. We are completely stuck at the station. They are announcing that diesel engines are coming to take the train forward."