Pakistan's prime minister called for emergency measures as the death toll from a heatwave in southern Sindh province reached nearly 700.

The National Disaster Management Authority (NDMA) said it had received orders from Nawaz Sharif to take immediate action, the BBC reported on Tuesday.

The army has also been deployed to set up heat stroke centres and assist the NDMA, it added.

Many of the victims are elderly people from low income families.

Health officials say many deaths have been in the largest city, Karachi, which has experienced temperatures as high as 45C (113F) in recent days.