Tokyo recorded 453 heat-related hospitalisations on Wednesday, the highest daily count since records began in 2010, the Tokyo Fire Department said on Thursday. One person died, four remain in critical condition and 18 are in a serious state in the prefecture, which is home to around 14 million people. Emergency services were deployed 3,612 times on Wednesday, a record since data collection began in 1963, according to a fire department spokesman.

The spokesman urged the public to stay hydrated and use air conditioners, noting that the number of patients rose as temperatures increased. The Japan Meteorological Agency (JMA) has issued heatstroke alerts for 41 prefectures stretching from Tohoku to Okinawa. The agency introduced a new term this year, “kokushobi” or “cruelly hot day”, for temperatures above 40 degrees Celsius, designed to draw greater public attention to heat-related warnings, although it does not trigger official measures nationwide.

Scientists say human-induced climate change is increasing the frequency and intensity of extreme heat events in Japan and elsewhere. Japan sweltered through its hottest summer on record last year, with the highest temperature ever recorded in the country — 41.8 degrees Celsius on 5 August 2025 in Isesaki, north of Tokyo. The Fire and Disaster Management Agency reported that at least 14 people have died from heat-related causes in the past week, and nearly 11,000 people sought emergency medical care nationwide.

The disaster agency said the public must regard the extreme heat as a “disaster”, adding that severe heat is expected to continue nationwide. In the central region of Aichi, which includes Nagoya, 116 people were taken to hospital on Wednesday. Four locations — one in Mie, two in Gifu and one in Shizuoka — saw temperatures above 40 degrees Celsius on the same day, according to the JMA. Meanwhile, the agency warned that moist air flowing into a weather front could cause unstable atmospheric conditions in northeastern Japan, with potential for heavy rain, thunderstorms, landslides and flooding.