Pakistan's prime minister has 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 army was also being deployed to set up heat stroke centres and assist the NDMA, it added.
Temperatures have reached 45C (113F) in recent days in the city of Karachi.
Sindh province Health Secretary Saeed Mangnejo said that 612 people had died in the city's main government-run hospitals during the past four days. Another 80 are reported to have died in private hospitals.
Many of the victims are elderly people from low-income families.
Thousands more people are being treated, and some of them are in serious condition.
The demand for electricity for air conditioning has coincided with increased power needs over Ramadan, when Muslims fast during daylight hours.
Hot weather is not unusual during summer months in Pakistan, but prolonged power cuts seem to have made matters worse, the BBC's Shahzeb Jillani reports.
Sporadic angry protests have taken place in parts of the city, with some people blaming the government and Karachi's main power utility, K-Electric, for failing to avoid deaths, our correspondent adds.
The prime minister had announced that there would be no electricity cuts but outages have increased since the start of Ramadan, he reports.
Source: BBC