May and June are India's hottest months, with temperatures regularly pushing above 40 Celsius. But meteorologists say the number of days when temperatures approach 45 Celsius has increased in the past 15 years.
The death toll in the worst affected states of Andhra Pradesh in the southeast and nearby Telangana is more than double the toll from a shorter hot spell there last year, officials said, with most of those killed elderly or laborers suffering sunstroke or dehydration.
The toll in Andhra Pradesh alone is 852.
Authorities have canceled doctors' leave and advised people not to head outside in the middle of the day to avoid the worst of the heat, but for many Indians, staying indoors is not an option.
"I get headaches, fever sometimes. But (if I stay indoors) how will I make money?" scrap collector Akhlaq, 28, said in the capital Delhi, where temperatures touched 45 Celsius on May 26.
The heat wave entered its sixth day in parts of the south. That's double the time they generally last, according to Y.K. Reddy, a government meteorologist in Hyderabad in one of the worst affected regions.
Blamed on dry continental air blowing in from Iran and Afghanistan, the heat wave is forecast to subside later this week before monsoon rains bring relief to parched areas of the east and south.