Pakistan has declared an emergency in state-run hospitals after the death toll from a sizzling heatwave rose to 47, while scores of heat-related deaths have been reported in neighbouring India.

In Pakistan, temperatures have soared to more than 50 degrees Celsius in some parts of central Punjab and southern Sindh provinces since Friday, the meteorological office said.

At least 21 people have died in Punjab province in the past 24 hours, including three in the provincial capital Lahore, health ministry official Amir Ali told AFP.

Five of them drowned when they jumped into rivers or canals to beat the heat.

Meanwhile in India, scores of people have died in a heat wave that struck the north of the country at the weekend, but officials say the count probably underestimates the death toll among the region's rural poor.

The Press Trust of India news agency says two new heat-related deaths were reported on Monday in the capital New Delhi, taking the toll in the last two days to 39.