Extremely hot weather is forecast for Japan's Kanto-Koshin region, including Tokyo, on Wednesday, with people there advised to stay alert for heatstroke.

The Meteorological Agency said a high-pressure system covering the region on Wednesday is driving up temperatures.

The daytime high is forecast to reach 36 degrees Celsius in Kofu City, Yamanashi Prefecture.

A high of 35 degrees Celsius is expected in central Tokyo, Yokohama City in Kanagawa Prefecture, Chiba City in Chiba Prefecture and Tsuchiura City in Ibaraki Prefecture.

The agency and the Environment Ministry issued heatstroke alerts for the prefectures of Kanagawa, Chiba, Ibaraki, Gunma and Yamanashi, as well as the Izu Islands of Tokyo.

Suspected heatstroke sufferers have been rushed to hospitals in recent days, with some dying.

People are advised to stay indoors, refrain from exercise, use air conditioners and consume adequate water and salt.

Close attention should be paid to senior citizens, babies and younger children, as they are especially vulnerable to extreme heat.

People planning outdoor leisure activities during the Bon holidays are advised to carry ice in water bottles and ice packs.

Atmospheric conditions have become extremely unstable in the Kanto-Koshin region due to soaring temperatures and warm, damp air. Rainclouds are developing over Tokyo, Chiba Prefecture, Ibaraki Prefecture and elsewhere. Heavy rains accompanied by thunder may hit these areas through Wednesday night.

Rainfall in the 24 hours through Thursday morning could reach 100 millimeters in Koshin and northern Kanto and 80 millimeters in southern Kanto.

Weather officials are warning of flooding in low-lying areas. They are also urging caution against mudslides and swollen rivers, as well as lightning strikes, hail and violent gusts, including tornadoes.