Almost entire Delhi went without power for about eight hours today due to the collapse of the Northern Grid, putting people to misery on a humid day when water distribution and Metro services were largely affected.

Top Delhi Power Department officials said the technical failure near Agra resulted in the collapse of the Northern Grid, which supplies electricity to Delhi, Uttar Pradesh, Punjab, Rajashtan, Haryana and Himachal Pradesh.

The main casualty of the power failure was the water distribution system as well as Metro services but operations at the airport remained largely unaffected as diesel generating back-up system was put to use.

Metro train services on all six corridors were affected since morning and the Metro was able to run trains only from 7 am, an hour later than the usual time of 6 am.

When the services began at 7 am, only 25 per cent of trains were put on all six corridors affecting commuters. The services were fully restored finally by 9 am.

As there was no power, all the water treatment plants in the city could not treat water, affecting the entire distribution system in the city.

Officials said various power generation plants running on hydel, coal and gas had to shut operations due to the failure and power supply could be fully restored in the afternoon.

"Delhi government or power distribution companies have no role to play in this crisis. It was a major technical fault in the Grid. We expect the situation to be normalised in the next four-five hours (by afternoon)," they said.

Delhi government officials said Power Minister Harun Yusuf is constantly monitoring the situation and officials are in touch with the Union Power Ministry and Power Grid Corporation, which maintains the Northern Grid.

Officials in the power discom companies said the areas under their jurisdiction had to suffer power cuts as supply was snapped.

As majority of the Metro trains were taken off services due to power failure, the frequency of trains dropped to an all-time low of 20 minutes on a few corridors in the first few hours in the morning.

Sources said that though the failure in the Northern Grid is expected to be rectified only in the evening, Delhi Metro was getting hydel power from Bhutan on priority basis along with power from AIIMS and Prime Minister's House to run the services.

As services were not available in the morning, people were forced to take over-crowded buses and auto rickshaws.

Passengers alleged that there were no proper announcements about the power failure at Metro stations.

Delhi Metro carries around 18 lakh passengers a day.

"It was a horrible night. It was a bit humid and without fans, it was difficult. The morning also proved disastrous as we could not get water as motors could not be operated," said Manjari Mishra, an office-goer.

The minimum temperature was recorded at 28 degree Celsius while the humidity was at 81 per cent.

A Delhi airport official said as soon as there was a disruption in power supply, all essential services like flight arrival and departure, check-in, baggage handling, aerobridge services were shifted to the back-up system.

However, there were reports of air conditioning not functioning in Terminal 1D and some portions of Terminal 3.

Also, there was no power in some retail outlets at the airport. "Overall ninety-five percent of our services remained unaffected", a spokesperson said.

"All flight operations at IGIA are normal with no cancellations and delays. The power supply was restored to DG Systems instantaneously and has been running smoothly," the spokesperson said.