Many parts of Japan saw the mercury top 30 degrees Celsius on Thursday. Weather officials are warning of unseasonal high temperatures over the weekend.
The Meteorological Agency says temperatures surged nationwide due to a high pressure system over the Japanese archipelago.
Kushima City, Miyazaki Prefecture, recorded a daytime high of 30.8 degrees -- the highest on record for the month of May.
The mercury also surged in northern parts of the country. The daytime highs reached 27.9 degrees in Obihiro City, Hokkaido, and 27.7 degrees in Aomori City.
Seven elementary school students in Mie Prefecture and five high school students in Tokyo were taken to hospital for suspected heatstroke.
Authorities are warning of heat-induced illnesses as temperatures are expected to rise further in the coming few days. Some areas will likely have a daytime high of 35 degrees on Sunday.
The Environment Ministry's website provides tips on how to fend off the hot weather, including making use of parasols.