Dozens of people are feared to have died in a heatwave gripping Pakistan's largest city Karachi this week, a charity in the sprawling metropolis said Tuesday, as temperatures hit 108F (42C).

The non-profit Edhi Foundation said scores may have been killed by the sweltering weather, with double the usual number of bodies sent to the city's morgues in recent days.

'We have received 180 dead bodies in the last four days which is more than double of what we receive normally,' said Faisal Edhi, head of the welfare organisation which oversees a variety of public health projects - including morgues and ambulance services.

People sleep on a pavement, to escape the heat and frequent power outages

A boy reacts as he receives a spray of cold water, to avoid the intense heatwave

'The majority of these were sudden deaths because of the heatwave as claimed by their relatives, which we cannot independently verify.'

The provincial government in Sindh province disputed the estimate.

'Only one casualty has been reported due to heat stroke so far,' said Muhammad Ali Shaikh, Director of the Provincial Disaster Management Authority in Sindh told AFP

The heatwave coincides with the beginning of Ramadan, when millions of devout Pakistanis abstain from food and drink from sunrise to sunset.

The Pakistan Meteorological Department warned 'hot to very hot weather is likely to prevail in Karachi during next 2-3 days', forecasting highs of 44 degrees Celsius during the period.

Aamir Habib, from Karachi's Korangi, said his brother was among the dead and had been rushed to the hospital after collapsing at work on Monday.

A leaking water pipe provides an opportunity for these people to get some relief from the heat

The broken pipe attracted a large crowd of people keen to escape the blistering heat

People resting from the heat in a mosque in Karachi, where temperatures reached 108F

Pakistanis cool off at the beach in Karachi, Pakistan's largest city

Volunteers adjust the dead bodies of heatwave victims at the Edhi Foundation morgue in Karachi

A bearded man gets a squirt of water in the face at a stall set up by a social welfare organisation

'The doctors said he died because of heat stroke,' Habib told AFP.

The mega port city, capital of southern Sindh province, is hit by frequent power cuts and has few green spaces.

People living on its crowded streets have little access to shelter or safe drinking water, making them acutely at risk in blistering temperatures.

In June 2015 about 1,200 people died in southern Pakistan during a heatwave, with nearly two-thirds of the victims homeless people.

Reports of heat stroke deaths in Karachi will stir unease amid fears of a repeat of a heatwave in of 2015, when morgues and hospitals were overwhelmed and at least 1,300 mostly elderly and sick people died from the searing heat.

Volunteers from Edhi Foundation give a cool shower to an elderly man

Bus passengers get a welcome spray of cool water to prevent heat stroke

Residents of Karachi sleeping on the pavement has become a common sight during the heatwave

A health official pours water on a man's head in a bid to prevent heat stroke

Men and children cool off from the heatwave, as they are sprayed with water coming out of a leaking water pipe

In 2015, the Edhi morgue ran out of freezer space after about 650 bodies were brought in the space of a few days. Ambulances left decaying corpses outside in sweltering heat.

The provincial government has assured residents that there would be no repeat of 2015 and was working on ensuring those in need of care receive rapid treatment.

Edhi said most of the dead brought to the morgue were working class factory workers who came from the low-income Landhi and Korangi areas of Karachi.

'They work around heaters and boilers in textile factories and there is eight to nine hours of (scheduled power outages) in these areas,' he said.