The sweaty weather has sent hundreds of people to hospitals and raised fears of an eventual power shortage, with Japan's largest nuclear power plant shut down since an earthquake last month.

At least 33 people have died this month in the heat wave, caused by high air pressure from the hot Pacific Ocean, according to a tally by public broadcaster NHK.

The mercury rose to 40.8 degrees Celsius (105.44 F) in Gifu prefecture in central Japan in midafternoon Friday, a day after it soared to a domestic record of 40.9 C (105.62 F) there, the Japan Meteorological Agency said.