The mercury is expected to reach 39 degrees Celsius (102 degrees Fahrenheit) on Monday in the city of Nagoya in central Japan and reach 37 (99 F) in Tokyo.
South Korea’s Yonhap news agency says the country’s highest-ever morning low was recorded in the city of Gangneung, where the temperature was 31 (88 F) at 6:45 a.m. The morning low in Seoul was 29 (84 F).
Hundreds of people have been rushed to Japanese hospitals with heat stroke symptoms in the more than week-long heat wave. Deaths have been reported almost every day.
Authorities in Japan warned people to stay inside and use air conditioning.