Clear sky over wide areas of Japan's main island of Honshu has pushed up temperatures above 30 to 35 degrees Celsius in many areas.
The intense heat is expected to continue through Saturday, putting people in the region at risk of heatstroke.
Japan's Meteorological Agency says the scorching weather is due to a high pressure system covering wide areas near Honshu on Friday.
The daytime high reached 35.9 degrees Celsius in western Japan's Kyoto City.
Temperatures rose to 34.1 degrees in the western city of Osaka, 33.3 degrees in the central city of Nagoya, and 31.7 degrees in central Tokyo and the western city of Hiroshima. The northeastern city of Sendai had a high of 30.4 degrees.
People should take steps to avoid heatstroke, as their bodies may not have adapted to the high temperatures at this time of the year.
Use an air conditioner, drink water frequently even you are not thirsty. Avoid long hours of work and intense exercise outdoors and take a rest appropriately.