The worst heatwave to hit Pakistan's southern city of Karachi for nearly 35 years has killed more than 1,000 people, a charity said on Thursday, as morgues ran out of space and residents rushed to supply over-stretched public hospitals.

Tents offering iced water and rehydration salts have mushroomed on street corners, run by rival political parties and the military.

Residents in one neighbourhood hacked into a main water pipe and then danced delightedly in the spray.

The heat wave in the city of 20 million people coincided with severe electricity cuts, leaving many without fans, water or light.

It also happened around the beginning of the holy month of Ramadan, when many Muslims do not eat or drink during daylight hours.

Some shops have refused to sell ice or water during the day, citing religious laws that mean they can be fined.

It is also illegal to eat or drink in public from dawn to dusk.

Temperatures shot up to 44 degrees Celsius at the weekend, the hottest since 1981, although they dipped on Thursday.

Forecasters have been predicting rain for days, but there has been no significant fall.

Hospitals in Karachi have been struggling to deal with the huge volumes of patients. ( Reuters: Akhtar Soomro )

An influx of dead means body bags have stacked up on the floor of the morgues, said Anwar Kazmi, a senior official of the charitable organisation the Edhi Foundation.

"The refrigeration unit was not working properly because there were too many bodies," he said.

Mr Kazmi said more than 1,000 people had died of heat-related causes so far.

The provincial government had done little except try to blame others, he said.

"We pay tributes to the doctors and staff of the government hospitals who are working tirelessly treating an endless number of patients," he said.

Hospitals called in student doctors to work extra shifts and appealed for basic items like sheets and stretchers.

Decades of chronic neglect by successive civilian governments or military regimes have gutted social services like health and education.

Many public hospitals said citizens dropped off carloads of iced water and other supplies.

The number of patients was slowly declining as the temperature goes down, doctors said.

Jinnah hospital had an overwhelming response to its appeal for cold water and stretchers, Dr Tasneem Butt said.

Reuters