KARACHI, Pakistan — Karachi’s poor learned long ago to cope with the many adversities that afflict Pakistan’s most crowded and chaotic city, including flooding, street violence and political crises. But since a suffocating heat wave descended on Karachi three days ago, killing at least 650 people, they have found no respite and no escape.
It’s so hot, said a security guard, Shamim ur-Rehman, 34, as he sat on a cot, looking beleaguered. There is no fan, there is nothing. I can’t sleep at night or during the day.
Prime Minister Nawaz Sharif declared an emergency on Tuesday as the death toll from the heat wave soared, with overwhelmed hospitals struggling to treat a surge of casualties and morgues filling to capacity. The army set up emergency treatment centers in the streets and the provincial government closed schools and city offices.
The Edhi Foundation, which runs an ambulance service and Karachi’s largest morgue, said it had collected over 600 bodies in recent days.
The first to die were the people on the streets — heroin addicts, beggars, the homeless, said Anwar Kazmi, a spokesman for the service. Then it was the elderly, particularly those who didn’t have anyone to take care of them.
In many ways, the emergency is the product of a perfect storm of meteorological, political and religious factors in Karachi.
Chronic shortages of water and electricity have exacerbated the impact of the heat wave, which has brought temperatures up to 45 degrees Celsius, or 113 degrees Fahrenheit, in a crowded city of 20 million people that is normally ventilated by a sea breeze.
The health dangers are further exacerbated by the demands of the annual Ramadan fast, when most Muslims abstain from eating or drinking water during daylight hours.
For most people, that means about 15 hours with no source of hydration — a factor that has particularly affected manual laborers and street vendors, who work outside under the sun.
Dr. Seemin Jamali, head of Jinnah Postgraduate Medical Center emergency wing, said 272 people had died there from heat-related conditions, including dehydration. The smaller Abbasi Shaheed Hospital said 56 bodies had been brought in since Monday night.
Officials said a majority of the victims were men over the age of 50, especially day laborers from lower-income groups.
Although Karachi residents are used to dealing with other emergencies — stockpiling groceries, for example, during bouts of street violence — they seemed at a loss for how to manage the extended heat wave.
The electricity shortages are the product of decades-long mismanagement of Pakistan’s national grid, and are often worse at dusk when many people are cooking in preparation for the end of the fast.
Not only do the power cuts make air-conditioning units and ceiling fans useless — they also reduce the water supply by shutting down pumps. Ice is in short supply and being sold for a premium in many neighborhoods.
As the death toll rose over the weekend, many residents opted to stay indoors or to congregate at centrally air-conditioned malls. But that was not a choice for laborers, who make as little as $10 a day and try to keep themselves cool by wrapping wet towels around their heads to stave off the sun.
Political anger over the crisis focused on the government of Mr. Sharif, who had pledged to reduce the energy crisis when he came to power two years ago.
Syed Qaim Ali Shah, the chief minister of Sindh Province, which includes Karachi, blamed the federal government for failing to get better results from K-Electric, the private company that runs the city’s electricity supply.
Mr. Sharif’s officials dismissed that criticism and tried to turn the blame back on Mr. Shah. Addressing Parliament in the capital, Islamabad, Khawaja Asif, the national minister for water and power, insisted he had no direct control over K-Electric.
On the streets, people blamed politicians of all stripes. Over the past year, Mr. Sharif’s government has frequently appeared impotent during moments of crisis. By contrast, the powerful military, led by Gen. Raheel Sharif, has become an increasingly assertive force in public life.
Amid the political finger-pointing, some news media commentators called on politicians to voluntarily cut off their own electricity and experience the hardship endured by ordinary people. Some journalists fell victim to the heat, too, like a cameraman who fainted during an official news conference in Karachi on Tuesday afternoon.
Most residents concentrated on escaping the suffocating heat. Television coverage showed residents fleeing their flats to seek shelter in the open streets.
We try and sit in the shade, said Mohammad Yusuf, 32, a laborer who works on a moving crew with a pickup truck. We went all the way near the port today and sat under a tree for three hours.
At Jinnah Hospital, Dr. Jamali said members of her staff had treated more than 5,000 patients from Saturday to Monday. The heat, not the fasting, was the principal factor in the deaths, she said.
Although many continued to fast, others quietly allowed that they were unable to cope with the demands of their faith. Subah Sadiq, a fruit vendor and father of seven, said it was impossible to stand in the street all day without drinking.
This is the only way to survive, he said.
Even for those not fasting, staying hydrated is a challenge: Under Pakistani law, in public places, eating and drinking are illegal during Ramadan, although some clerics said their followers could break the fast if their health was in danger.
Mr. Rehman, the building watchman, was refusing to give up.
As long as I have some life in me, and strong intentions, I will fast, he said.
One small glimmer of good news came from the weather service. Although hot weather is forecast to continue through this week, officials said, a small amount of rainfall was predicted for Karachi and surrounding cities for late Tuesday night.
Correction: June 23, 2015
An earlier version of this article misstated, at one point, the surname of a doctor who is head of the Jinnah hospital’s emergency wing. As correctly noted earlier, she is Dr. Seemin Jamali, not Jilani.
Saba Imtiaz reported from Karachi, and Declan Walsh from London.