A day after a major power breakdown plunged the entire country into darkness, electricity supply was restored in most cities and towns by Sunday evening. Energy Minister Omar Ayub said in the morning that power was expected to be completely restored soon.

The blackout was reported a little before midnight by citizens on social media from across the country, including major urban centres such as Karachi, Islamabad, Lahore and Multan, as well as smaller towns and cities.

In a tweet in the evening, the Ministry of Energy said power supply had been fully restored to the grid stations of the Peshawar Electric Supply Company (Pesco) that were impacted by last night's breakdown. It said grid stations operations teams had remained busy in restoration efforts through the night to protect the system from overloading.

The ministry further said load-management of limited duration was being carried out on different feeders of Peshawar, Khyber, Mardan, Swabi, Swat and Hazara circles, adding that uninterrupted power supply will be restored for all affected areas soon.

Meanwhile, the K-Electric, which is the sole power distributor in Karachi, also said most parts of Karachi had been re-energised by Sunday evening.

"Since 12am last night, KE teams have been working to restore power rapidly to affected parts," the power utility said in a statement, adding that KE's transmission and distribution networks were swiftly restored along with power generation from KE's Bin Qasim power plant and IPPs.

"By late evening, supplies from the national grid were also resumed through existing interconnection points with K-Electric. Most parts of Karachi have been energised already, while teams are available to address any individual customer complaints received at its 118 call centre," it added.

Addressing a press conference in Islamabad earlier in the day, Ayub said that investigations were ongoing to ascertain the cause of the breakdown at Guddu power plant that had plunged the country into darkness.

"We don't know the reasons at this time since we'd sent teams at night to Guddu [power plant] and there was a lot of fog, nothing could be seen at the time [...] as the day goes on and the fog clears, the investigation will be conducted [to ascertain] where the fault occurred."

Ayub said that at 11:41pm on Saturday, the Guddu power plant developed a fault and "within a second, the frequency dropped". He further explained that in technical terms, this is called a cascade effect, since "one after the other" the safety systems of the power plant began to shut down.

The minister said that this was similar to a fuse blowing which has to be manually reset, and the power plant being shut down had affected the entire country.

The energy minister said that it will take a few more hours for the electric grid to be completely restored, adding, however, that power supply had already resumed in many cities. He said that the Tarbela power plant was fired up soon after the breakdown, following which power supply was restored to Islamabad, Rawalpindi and half of Lahore.

Other cities in Punjab like Jhang, Mianwali and Multan "to a large extent had been energised", while a supply of 400 megawatt was released to K-Electric for Karachi, he added.

System failure

Earlier, the Ministry of Energy spokesperson, tweeting from the ministry's official Twitter handle, said that according to initial reports, the Guddu power plant developed a fault at 11:41pm on Saturday night.

“The fault caused the country’s high transmission lines to trip, which in turn caused the system frequency to drop from 50 to 0 in less than a second.

The drop in frequency caused power plants to shut down.”

Some time later, the energy minister tweeted that power supply was being restored to cities in phases, starting with Islamabad.

According to Ayub, the power breakdown was caused after the frequency in the national power distribution system suddenly fell from 50 to zero.

Restoration efforts

By late morning, power had been restored to some areas of major cities such as Lahore, Islamabad and Karachi, authorities announced on Twitter.

"132kv Grids Around Lahore Energized," Ayub tweeted just before 8am.

The K-Electric also said that power was being restored in phases to the port city.

Engineering teams are making "full efforts" to restore electricity supply, the utility service provider said on Twitter.

There were no immediate reports of disruption at hospitals, which can often rely on back-up generators.

AFP quoted a water and power ministry spokesman as saying that power had been restored to some parts of the country but many areas in Lahore and Karachi were still waiting.

Netblocks, which monitors internet outages, said internet connectivity in the country “collapsed” as a result of the blackout.

Connectivity was at “62 percent of ordinary levels,” it said in a tweet.

With additional reporting by Imtiaz Ali in Karachi.