The Ministry of Economy, Trade, and Industry issued the warning in anticipation of a spike in electricity demand, particularly between 4 to 7 p.m. local time on Monday, when the temperature is expected to be at its peak.
It stated that while electric suppliers across Japan have agreed to increase supply capacity, the power supply may still be insufficient to meet demand if temperatures continue to rise.
“If there is an increase in demand or a sudden power supply trouble, the reserve margin will fall below the minimum required of 3 percent, and there is a possibility that a power supply and tight demand will occur,” it stated.
Reserve rates for energy supply and demand in Tokyo are expected to be 4.7 percent between 4 and 4:30 p.m. local time, then decline to 3.7 percent between 4:30 p.m. and 5 p.m., according to the ministry.
The government advised all households to conserve power by turning off lights not in use, limiting the use of air conditioners, and guarding against the risk of heat strokes.
Japan’s Meteorological Agency also warned of “extreme weather” on Monday. At 1 p.m. local time, the temperature in downtown Tokyo was 34.7 degrees Celsius (94.46 degrees Fahrenheit), while the temperature in Sano reached 38.6 degrees Celsius (101.48 degrees Fahrenheit).
Weather officials said the annual rainy season had ended earlier than usual across much of Japan, including the Tokyo metropolitan area, since the Japan Meteorological Agency began keeping records in 1951.
Summer heat in Japan starts with the end of its rainy season. In 2018, the rainy season ended with an extremely hot summer with several heat waves that put thousands in hospital.
Reuters contributed to this report.