People across Japan have endured another day of punishing heat, with temperatures on Friday reaching more than 38 degrees Celsius in the northern regions of Hokuriku and Tohoku.

Observation sites further north registered their highest temperatures on record.

The summer in Hokkaido is usually mild, but now the heat is breaking records. In the city of Sapporo, the mercury hit 34.7 degrees Celsius.

Hokkaido Railway Company cancelled some trains because the heat could bend tracks.

Monkeys at a botanical garden in the city of Hakodate were given ice blocks for the first time to cool them down, as they were losing their appetite in the heat.

A high school in Sapporo held classes online to guard the students against heatstroke. The teachers broadcast lessons from classrooms that are do not have air conditioning.

Miyahara Yusuke, Vice principal at Sapporo Shinyo High School, said, "This is disaster-level heat. We went online because we were worried students would get sick at school or while traveling if we made them come in."

On Friday, more than 760 public and other schools in Hokkaido suspended classes or finished earlier than usual.

The heat is a challenge for nursing homes as well. The only air conditioning at this home is in shared spaces. Staff turned down the temperature to 25 degrees and used fans to blow the cool air into other rooms.

The heat is also affecting eateries. A bakery in the northeastern city of Akita had to stop making most of its cakes. The staff couldn't use fresh cream because it wouldn't stay firm in the heat.

Akita Prefecture has had extreme heat for days. On Thursday, two people thought to have suffered heatstroke were found dead. The temperature in the towns where they died was more than 35 degrees Celsius. Both places had issued heatstroke warnings.

Japan this year had the hottest July since weather officials began keeping records in 1898.

The heat and its effects are also monitored by a company called Weathernews. One phenomenon was highlighted in its survey last summer.

Three quarters of respondents across Japan said they were seeing fewer mosquitoes.

Sunahara Toshihiko, Assistant Professor at the Institute of Tropical Medicine of Nagasaki University, explained that the extreme heat makes mosquitoes less active and pushes their survival rates down.

"The heat in recent years has not been suitable for mosquitoes to survive. When the temperature reaches about 35 degrees Celsius, they stop flying," Sunahara said.

But he added that people should not let their guard down.

"The number of mosquitoes could increase from September to October, when the heat subsides. So people should be careful," Sunahara said. "It won't just be a good season for people. It will be good for mosquitoes, too."