Karachi: Pakistan's worst heatwave in decades has claimed at least 630 lives in the country's largest city as authorities on Tuesday ordered closure of all educational institutions and government offices and the army has also been called in to deal with the situation.

The heatwave, sweeping across Sindh province, has been going on since the start of Ramzan on Friday, wreaking havoc and triggering an emergency situation in major hospitals of the province. The death toll in worst-hit Karachi has topped 630 with another eight to 10 people dead in other parts of southern Sindh as a result of soaring temperatures, a senior health official was quoted as saying by media reports.