According to reports in some areas of Islamabad and Rawalpindi power supply has been restored while most of the parts of the city were still in darkness.
A large part of Khyber Pakhtunkhwa province has also been deprived of electricity for several hours.
A spokesman of the Water and Power Ministry has said tht NTDC engineers had managed to temporarily fix the transmission line, which suffered major fault earlier today.
Power was temporarily restored to several parts of KP and Punjab at the time of filing of this report, while engineers were working to restore supply to other affected areas.
According to officials of the water and power ministry at around 11:00 am, a technical fault appeared in the Tarbela Power plant, which also caused the Northern Transmission line to trip.
Islamabad, Gujranwala, Sargodha, Lahore and scores of northern Punjab cities descent into darkness for several hours due to the fault in the electricity transmission system.
The ministry of water and power in a statement said that the power supply to the affected cities being restored, which was disrupted due to the fault in Tarbela Dam power transmission line.
Moreover, electric switches tripped at the switchyard of Guddu Power Plant in Kashmore district of Sindh.
According to sources, these switches were changed six months ago.