Tens of millions of people in Pakistan were left without electricity on Monday, the power ministry said, reporting a second "major breakdown" of the national grid during the last three months.

Factories, hospitals and schools across the country were without power for hours after a voltage fluctuation in the grid occurred between the cities of Jamshoro and Dadu in southern Sindh province, power minister Khurrum Dastagir said.

"There was a fluctuation in voltage and the systems were shut down one by one. This is not a major crisis," Dastagir told Geo TV news channel.

Outages were reported in the southern port city of Karachi, the capital Islamabad, the eastern city of Lahore and Peshawar in the north.

The sorry state of Pakistan's power sector is emblematic of an economy that has lurched from one International Monetary Fund bail-out to the next, with electricity outages occurring frequently due a lack funds to upgrade aging infrastructure.

When the grid broke down in October it took several hours before power was restored.

In Peshawar, a city of more than 2.3 million people, some residents said they were unable to get drinking water because the pumps were powered by electricity.

Mohammad Asim, a spokesman for the city's Lady Reading Hospital, the largest in Khyber Pakhtunkhwa province, said back up generators were used to provide uninterrupted electricity for the emergency ward, intensive care units, and laboratories.