Temperatures broke 35 degrees in many parts of the nation Sunday, causing the death of one man and sending at least 609 other people to hospitals for overheating, a survey says.
In the city of Shikokuchuo in Ehime Prefecture, a 50-year-old man was taken to a hospital and later confirmed dead, apparently due to heatstroke.
A high-pressure system over the Pacific Ocean carried in warm southerly winds, raising temperatures from Kyushu to Hokkaido.
The Tokyo metropolitan area saw the mercury pass 35 for the first time this summer as the Otemachi business district hit 35.4 the same day.
Further north, in Mie Prefecture, the city of Owase hit 37.0, the Meteorological Agency said.
Heat stroke can usually be confirmed by a core body temperature above 40.5 degrees, but fainting may also be a tip-off. Other symptoms include headache, dizziness, failure to sweat, cramps or nausea, a rapid pulse or breathing, or even seizures.
High temperatures were also recorded in western and southwestern Japan, with Kasama in Ibaraki Prefecture, and Tajimi in Gifu hitting 36.2 and 36.1, respectively. Koshigaya in Saitama and Higahsiomi in Shiga reached 35.9 and 35.6 degrees, respectively.
Even in Hokkaido, the town of Ikeda recorded a temperature of 33.9 while the cities of Obihiro and Kushiro saw the mercury hit 33.6 and 32.7, respectively — more than 10 degrees higher than average.
The agency said temperatures on Monday will rise across the nation — especially in Tokyo, Saitama, Gifu and Nagoya — and called on the public to take precautions against heatstroke.
According to local police and fire stations, 10 junior high school students, who were taking part in a baseball game in Saitama were taken to a hospital after exhibiting symptoms of heatstroke.
Marathoners were also affected, with six in Aomori Prefecture and some in Tottori hospitalized.
Off the coast of Matsuyama, Ehime Prefecture, a 15-year-old boy drowned, while in Gifu, a 10-year-old girl and her 4-year-old brother disappeared in the Hida River in the city of Gero.
Both siblings were swept away when the girl tried to rescue her brother after he slipped into the river.