A senior Pakistani health official says the death toll in the country's southern Sindh province, which has been struck by a heat wave, has reached 622.

Senior provincial health official Saeed Mangnejo said on Tuesday that he expects the number of fatalities to climb further.

Mangnejo says the death toll is for the past three days, though most of the deaths were reported in the province's largest city, Karachi.

Temperatures reaching 113 degrees Fahrenheit struck Karachi over the weekend. Hours-long power outages also hit the city, leaving fans and air conditioners inoperable.