Thousands of others have reportedly been hospitalized for heat-related illness.
Temperatures in central Tokyo hovered around 99 degrees Fahrenheit on Monday, with temperatures rising above 100 degrees in some parts of the country.
The Japan Meteorological Agency said in a statement that the potential for heat-related illness is higher than usual and people should take precautions like drinking a lot of water and staying away from direct sunlight.
AccuWeather reports normal high temperatures in some parts of Japan are in the mid to high 80s.
Additional reporting from Newsy affiliate CNN.