After hours of blackout due to a breakdown of the Northern Grid early on Monday, power supply was restored to almost 80 per cent areas of Delhi by noon, officials said. Delhi blamed Haryana, Punjab and Uttar Pradesh for overdrawing power that caused the grid's collapse.

"At 2:33 a.m. the frequency was very low at Northern Grid and it collapsed. Haryana, Punjab and Uttar Pradesh were drawing between 2,500 and 3,000 mega-watts," Delhi's Power Minister Haroon Yusuf told reporters here.

A failure in the Northern Grid at 2.32 a.m. affected supply to seven northern states, including Delhi. Officials said the failure took place somewhere near Agra, causing the entire system to trip.

Power supply was also hit in Punjab, Haryana, Himachal Pradesh, Uttar Pradesh, Rajasthan, and Jammu and Kashmir.

"Power supply has been restored nearly 80 percent of Delhi," an official from Delhi power supplier BSES told IANS.

Yusuf also said by 4 a.m. electricity was restored at Delhi airport, the Prime Minister's House, and All India Institute of Medical Sciences (AIIMS).

"In the past ten years, this was an unprecedented power failure and we will make sure that such outages do not occur in future," Yusuf said.

Train services on the 190-km Metro network weaving through the length and breath of the national capital were affected due to the failure of the Northern Grid.

However, all Delhi Metro services could be restored only after two hours around 8.45 a.m. No Metro train ran from 6 a.m., when the services normally begin, till 7 a.m. Only 25 percent of the services were restored by 7 a.m.

"Services in all the six lines became normal by 8.45 a.m. We are receiving hydel power from Bhutan on priority basis," a Delhi Metro official said. He added that Delhi Metro was amongst the emergency services, including the Prime Minister's HOuse and AIIMS, that were provided power.

According to union Power Minister Sushilkumar Shinde, nearly 60 percent of electricity supply was restored by early morning and efforts were going on to restore the power supply "on a war footing".

Northern Railways, Delhi Metro and other vital services such as water treatment plants were affected.

The power outage led to an acute water problem across Delhi with taps running dry.

Power failure put the traffic signals on a blink, causing massive traffic jams during peak office hours.

V.V. Sharma, general manager of Power System Operation Corporation Limited (PSOCL), told IANS that power restoration work was going on and the situation was now "good" in most states.

He said a three-member committee has been appointed to look into the reasons of the power failure, and details would be given once the committee gives its report.

"The trouble resulted in power outage in the entire northern region, but for parts of Badarpur in south Delhi, Narora and Simbhauli in Uttar Pradesh and Bhinma in Rajasthan," a statement from PSOCL said.

According to a Northern Railway spokesperson, nearly 100 trains were disrupted but traffic was back to normal by 8 a.m. Around 45 local trains in Delhi were also affected.

"Power supply has resumed, but several trains are plying four-five hours late. We are holding back goods trains and giving priority to passenger trains," the spokesperson said.

"Vital services and VIP areas were first provided power, and most of the services have now been restored," a BSES official told IANS.