A spokesperson from the Sindh province Ministry of Health told CNN that 323 people had died in Karachi as a result of the heatwave.
The ministry also told CNN that the number of patients treated for heat stroke in Jinnah hospital, the largest in the city, is 2.360.
Others, unable to make it to a hospital, may have died at home. At least one city morgue, CNN affiliate Geo.tv has reported, has been overwhelmed with the numbers of dead.
Death tolls in local media reports vary.
The Sindh provincial government has declared a state of emergency in all its government hospitals, canceling leave of medical personnel and bringing in further medical supplies.
