Teachers and education officials are calling for students to pay special heed to the risk of heat exhaustion this summer, as many schools across Japan shorten their summer holidays and hold more classes than usual to make up for closures due to the novel coronavirus pandemic.

"Wearing masks is effective in curbing the spread (of the virus), but I would like (schools) to prioritize their responses to heat exhaustion," education minister Koichi Hagiuda told a news conference on Friday.

Temperatures have risen rapidly in recent days, prompting the central government on Thursday to issue a warning for heat exhaustion covering Tokyo and two surrounding prefectures, the first alert since the launch of a new system in July.

In June, the education ministry instructed prefectural education boards to take measures to avoid heat-related incidents during school days in August, including recommending that students carry water bottles on their way to and from school.

Officials of the Okayama Prefectural Board of Education called for schools in the western Japan prefecture to be flexible in their responses to the coronavirus.

"There are times when (schools) should prioritize steps to counter heat exhaustion over new life styles" amid the pandemic, the board said, asking teachers to allow students to remove face masks when they feel hot and find it hard to breathe.

It also urged them to ventilate classrooms, while properly using air conditioners to lower temperatures.

Prefectural junior and high schools in Okayama will break for summer holidays between Aug. 8 and 16, 34 days fewer than last year.

The shorter summer holidays stem from Prime Minister Shinzo Abe's call for schools nationwide to shut from early March as part of the government's anti-virus efforts, a measure that continued beyond April when Japan's school calendar starts.

In Kumagaya, Saitama Prefecture, which logged a national record-high of 41.1 C in 2018, the city education board is encouraging elementary school pupils to use umbrellas as parasols, maintaining social distancing at the same time.

In Takarazuka, Hyogo Prefecture, a bereaved relative of a junior high school student who died of heatstroke in 1999 requested that teachers and school officials exercise caution as students emerge from restrictions imposed earlier this year to prevent the spread the virus.

"Encouragement by teachers to take off masks, drink water and not to endure the heat will prevent heatstroke," said 62-year-old Katsuya Miyawaki, whose son Kento died at age 13 during rugby training.