Officials in Karachi said much of the city of 10 million people had been without power for more than 12 hours after a severe storm on Saturday.
Syed Sultan Hasan, a spokesman for Karachi's power utility, said: "We are doing our best to restore power supply, but I must say the situation is very bad."
Some people were electrocuted as power lines fell, while others were crushed as houses collapsed.
Weather officials predicted more rains for Sunday.
Meanwhile, aid operations are under way to provide food and water to thousands of people displaced by floods in India.
|Many areas of Mumba, India, |
were flooded to waist-level [AFP]
In the state of Andhra Pradesh, officials on Saturday put the death toll there at 35 and said 200,000 people had been made homeless by two days of rain.
Preeti Sudan, Andhra Pradesh's disaster management commissioner, said: "Soldiers and naval helicopters have taken up rescue operations in Kurnool and Guntur districts ... where people are stranded on rooftops and up trees."
Almost 200mm of rain has fallen on the state since Thursday.
Sudan said food and water packages were being distributed across 300 relief centres in the state, where rains have since eased.
"By tomorrow the situation should be absolutely normal... We are trying [to ensure] that [evacuees] return by tomorrow evening or by the day after tomorrow," she said.
In Mumbai, India, at one least one person was killed as around 300mm of monsoon rains flooded homes and streets.
Water was waist deep in many low-lying neighbourhoods.
Indian media reported that about 50 people had died in monsoon rains in the western state of Maharashtra over the past three days.
Most of those who died were either the homeless or poor farmers.
In the southwestern state of Kerala, about 20 people have died over the past two days.
Officials said 5,000 medical teams were touring areas affected by flooding in an attempt to prevent outbreaks of disease.
In northern Bangladesh, about 30 people have died of water-borne diseases over the past week after floods in the Brahmaputra river region.