Intense heat gripped much of eastern and western Japan on Thursday, with daytime highs rising above body temperature in a number of places.
The Japan Meteorological Agency said a high-pressure system intensified over eastern and western Japan, bringing the regions under a blazing sun.
The highest temperature of the day, 39.3 degrees Celsius, was recorded in Shizuoka City. That was the highest for the city since record-keeping began in 1940.
Aichi Prefecture's Nagoya City and central Tokyo both saw the mercury hit 35 degrees for the first time this summer.
The Tokyo Metropolitan Fire Department said that as of 3 p.m., 47 people had been taken to hospital with suspected heatstroke.
Aichi Prefecture officials had also reported 47 suspected cases of heatstroke as of 3 p.m.
The Meteorological Agency warns that temperatures are expected to stay above 25 degrees overnight in much of eastern and western Japan.
These regions can expect another sweltering day on Friday. The mercury is forecast to hit 37 degrees in Kumagaya City in Saitama, Kofu City in Yamanashi, Gifu City, and Toyooka City in Hyogo. A daytime high of 35 degrees is forecast for central Tokyo.
The Agency says the heatwave is likely to continue through Monday in western Japan, and may last until next Thursday in Amami, Kagoshima Prefecture, and Okinawa.
The Agency is asking people to take health precautions, particularly the elderly who are vulnerable to heatstroke.
People are advised to keep air conditioning running at night, and to have water at hand to stay hydrated.
The Agency is also advising people to regularly check a heat index on a government website. It says they should avoid exercising outside and at indoor facilities that do not have air conditioning.