Pakistan suffered a huge power cut early on Monday following a breakdown in its national electricity grid, the energy ministry said.
Power was out in all the country's major cities, including the biggest city Karachi, the capital Islamabad as well as Lahore and Peshawar.
Power minister Khurrum Dastagir said the grid failure followed a "frequency variation" in southern Pakistan.
He insisted this was "not a major crisis" and power would be back soon.
In a statement. the energy ministry said that at about 07:30 local time (02:30 GMT) the grid "experienced a loss of frequency, that caused a major breakdown", adding that "swift work" was taking place to revive the system.
Some grids in the country had already been restored and power would be fully restored in 12 hours, Mr Dastagir told Geo TV.
"In winter, the demand for electricity reduces nationwide, hence, as an economic measure, we temporarily close down our power generation systems at night," he said.
When they were turned on in the morning, "frequency variation and voltage fluctuation" were observed in southern Pakistan "somewhere between Dadu and Jamshoro" and subsequently "power generating units shut down one by one", he told the TV channel.
Earlier this month the government has ordered shopping centres and markets to close early every day to save money on power.
Pakistan's reserves of foreign currency have been falling and the country generates most of its power using imported fossil fuels.
Global energy prices jumped last year, putting further pressure on the country's already dwindling finances.
