An intense heat wave is gripping Japan, with scorching temperatures reaching life-threatening levels. The mercury hit almost 40 degrees Celsius in some parts of the country, sparking concerns over heatstroke.

Firefighters had to be called to a Kyoto water purification plant after the hot weather disrupted a school field trip. Authorities say nine students showed symptoms of heatstroke. Three were taken to a hospital.

In Tokyo, 55 people had to be rushed to hospital with similar symptoms as of 3 p.m. on Friday.

The extreme heat has proven fatal in some areas. A man in his 70s in Saga Prefecture was found dead inside his home after cutting grass. Another, in his 80s, died after collapsing at a farm in Shiga Prefecture.

Temperatures Friday exceeded 35 degrees across much of the country, as people tried to stay cool. Matsusaka, in central Mie Prefecture, saw a daytime high of 39.7 degrees, the highest on record for that city.

Japan's Meteorological Agency says dangerously hot conditions are forecast to continue through the weekend. People are advised to avoid going outside as much as possible, and to use air conditioners responsibly.