As temperatures in parts of India soared past 118 degrees Fahrenheit, officials reported at least 500 deaths so far in what is shaping up to be one of India’s worst heat waves.

The heat-related fatalities reported so far were concentrated in the states of Andhra Pradesh and Telangana in the south of India. But the capital city of New Delhi and the states of Uttar Pradesh and Rajasthan to the north were also suffering through record, life-threatening temperatures.

Estimates of the number of dead were rough. Historically, the full toll of India’s increasingly torrid heat waves are not known for months or even years, if at all, as scientists compare normal death rates with those during spikes in temperature.

The BBC put the number of dead so far at 500, with 246 of them in Andhra Pradesh just this week. Officials said 62 people died of sunstroke Sunday, the BBC reported.

India is always hot at this time of year. But, according to the Indian Express, temperatures are 5 to 6 degrees Celsius above normal. New Delhi hit 44.5 degrees Celsius, or 112 degrees Fahrenheit, over the weekend.

“Almost all the victims are old,” Telangana Principal Secretary B.R. Meena told the Indian Express. “Inquiries reveal that most of them were working and were exposed to the heat. Dehydration and heat stroke caused the deaths.”

According to a 2000 study by the Indian Institute of Science, average annual loss of human life attributed directly to heat waves in India is 153. But the real toll is much higher, according to studies, because the conditions tend to take a severe toll from the millions already suffering from respiratory and heart conditions.

And heat waves are increasing as a result of global climate change, according to the India Meteorological Department. Over the past half century, from 1961 to 2010, heat waves (when the temperature exceeds the average by 5 or 6 degrees Celsius) have increased by a third.

A heat wave in Ahmedabad in 2010, with temperatures reaching 112 degrees Fahrenheit, caused an “excess mortality” of about 1,300 people, according to a study done in 2014. 

A heat wave in Andhra Pradesh in 2003 — still considered perhaps the worst in recent years — claimed more than 3,000 lives.