Heat-related illnesses have claimed 11 lives and sent nearly 6,000 others to hospitals in Japan as the mercury rose following the end of the rainy season, according to the government on Tuesday.

The heatwave saw 5,664 people taken to hospitals, 1,199 of whom displayed severe symptoms requiring at least three weeks of treatment, and 1,792 requiring shorter treatment for less serious symptoms.

The total number, however, spiked from 2,000 people hospitalised across Japan a week earlier due to the heat.

On Tuesday, temperatures continued to soar and the agency and weather officials warned people to take preventative measures against heatstroke and other heat-related illnesses, Xinhua news agency reported.

Tajimi in Gifu Prefecture, central Japan, saw the mercury rise to 37.1 degrees Celsius, while Kumagaya in Tokyo’s neighbouring prefecture of Saitama and Kyoto saw temperatures rocket to 36.8 degrees Celsius.

In Tokyo, the daytime high was logged at 35.4 degrees Celsius. Temperatures across Japan are expected to stay above 25 degrees Celsius overnight.

In the week to last Sunday, the Fire and Disaster Management Agency said 52.6 per cent of the people hospitalised were aged 65 and above.

Aichi Prefecture saw the most people rushed to hospital with 393 cases, followed by Osaka Prefecture with 388 cases. Tokyo, meanwhile, saw 299 people rushed to hospital suffering from heat-related medical conditions.

Across wide swathes of Japan from north to south, temperatures were forecast to remain upwards of 36 degrees Celsius through Wednesday, weather officials said.