Heatstroke cases in Japan have shot up in the early summer as many air-conditioners have been switched off amid an energy saving campaign following the Fukushima nuclear disaster.
More than 13,000 people were rushed to hospital by ambulance in June and the beginning of July, data from the Fire and Disaster Management Agency showed. Twenty-six of them died.
The rise for June alone was three-fold from last year. Of all the heatstroke cases, more than half were over 65 years old.
The sharp rise came amid a sweltering heatwave, when the average temperatures in late June in eastern and western Japan hit their highest levels since such data were first kept in 1961, the agency said.
The mercury in late June topped 35 degrees Celsius (95 Fahrenheit) in hundreds of spots across Japan, and the average temperature was about 3.5 degrees Celsius higher than usual, the country's meteorological agency said.
The Fire and Disaster Management Agency is urging people to keep room temperatures no higher than 28 degrees Celsius and drink plenty of water. It warned that elderly people need to be cautious even when they stay indoors.
Only 19 of Japan's 54 nuclear reactors are operational four months after the March 11 quake and tsunami disaster sparked the world's worst nuclear accident since Chernobyl 25 years ago at the Fukushima Daiichi plant.
The government has asked the nation to save power, and homes and companies in the northeast are being asked to cut back usage by 15 percent in the summer, leading many to cut down on power-guzzling air-conditioners.
Explore further: Why your laptop battery won't kill you