hree cities in central Japan saw temperatures of 40C (104F) or higher on Tuesday, marking the country's first officially designated "kokushobi," or "cruelly hot day," since the Japan Meteorological Agency introduced the new heat warning category earlier this year, according to Kyodo News.

Tajimi and Gujo in the Gifu Prefecture saw temperatures of 40.3C (104.5F) and 40.0C (104F) respectively, while Toyoda in the neighboring Aichi Prefecture reached 40.1C (104.2F), the agency said

The term "kokushobi," introduced in April, applies to days when temperatures reach at least 40C (104F) and is intended to strengthen public awareness of life-threatening heat conditions.

The weather agency said a strong high-pressure system covering much of the Japanese archipelago since Sunday has warmed both surface and upper-level air, driving temperatures sharply higher.

As of mid-afternoon, 731 of Japan's 914 weather observation points had recorded maximum temperatures of 30C (86F) or above. Of those, 272 were classified as "moshobi," or "extremely hot days," while the three 40C (104F) readings were separately categorized as "kokushobi."

Other major cities also experienced intense heat, with Nagoya reaching 39.7C (103.5F) and Kumagaya in the Saitama Prefecture hitting 38.6C (101.5F), according to Kyodo.

The meteorological agency warned that dangerously high temperatures are expected to persist across many parts of Japan on Wednesday and urged residents to take precautions against heat-related illnesses, including staying hydrated, avoiding prolonged outdoor exposure, and using air conditioning where possible.

Japan issues heatstroke alerts for 41 of 47 prefectures

The dangerous conditions carried into the following day, as Japan on Wednesday issued heatstroke alerts for 41 of its 47 prefectures.

Japan is sweltering under an ongoing heat wave, with a lingering high-pressure system pushing temperatures above 40C (104.0F) for a second consecutive day, said public broadcaster NHK.

This marks the second straight day of "kokushobi," or "cruelly hot day," an official new designation to help underline the public warning.

The highest temperature was 40.5C (104.9F) in Kuwana, in the Mie Prefecture, followed by 40.1C (104.1F) in Hamamatsu, in the Shizuoka Prefecture, at 2 pm local time.

Several other cities also saw temperatures above 39C (102.2F).

According to the Tokyo Fire Department, 287 people were taken to hospital due to suspected heatstroke on Tuesday.

Residents have been advised to use air conditioners, stay hydrated, and maintain adequate salt intake. They were also urged to avoid prolonged outdoor activity.

The "kokushobi" category was introduced by the weather agency this year for days when temperatures reach 40C (104.0F) or higher, according to The Japan Times.

Last summer, more than 100,000 people were taken to the hospital for heatstroke.