"This time, the heatwave began a bit early. It is very strong," said Tahir Ali Javed, Health Minister for central Punjab province, where 35 people have died from heatstroke in the last week alone.

"The deaths are taking place at many places and we can't give you the exact numbers," he said.

The largest hospital in the eastern city of Lahore, Services Hospital, had received up to 20 patients a day from early this month, mostly students, suffering from diarrhoea, dehydration and vomiting, hospital doctor Mohammad Imran said.

The provincial health ministry issued circulars to educational institutions telling pupils to stop playing outdoor games.

"Children and elderly people are most vulnerable and we are trying to create public awareness of how to avoid heatstroke deaths," Javed said.

Temperatures of 50 Celsius have been recorded in Jacobabad and Nawabshah, two towns in southern Sind province, and in Sibbi in southwestern Baluchistan province, where several deaths have also been reported.

Similar heatwave conditions have been reported from northern India and schools have been closed early for the summer holidays.

Weather forecasters saw little chance of the heat abating in the coming weeks.

"There might be light rains with dust storms, but no significant showers, and above normal temperatures will persist for the rest of the month," Qamar-uz-Zaman Chaudhry, Director-General of the Pakistani Meteorological Department, said.

The silver lining was that glaciers in Pakistan's northern mountains will melt faster to help replenish reservoirs, Chaudhry said.

Pakistan, a country of 160 million people, relies heavily on winter rains and snow in the northern mountains to enable reservoirs and irrigation canals cope with demand during the dry months ahead of the monsoon.

Last winter, the country received 40 percent less than normal rainfall and up to 25 percent less snowfall.