The Tokyo Fire Department said 453 people were taken to hospital on Wednesday, the highest daily count since records began in 2010.
The number of times emergency services were deployed that day also hit a 63-year high.
“We are urging people to stay hydrated and use air-conditioners,” a fire brigade spokesman said on Thursday.
“It seems like the number [of patients] rose as the temperature rose. It seems like yesterday [Wednesday] and the day before yesterday, we really saw notable increases.”
He said one person had died, with four others in a critical condition and 18 in a serious state in Tokyo prefecture – home to around 14 million people.
In the entire central region of Aichi, which includes Nagoya, 116 people were taken to hospital on Wednesday for heat-related conditions, officials said.
The same day four locations – one in the Mie region, two in Gifu and one in Shizuoka – saw temperatures above 40 degrees Celsius, according to the Japan Meteorological Agency.
Japan introduced this year a new term to describe heat above 40 degrees called “kokushobi”, which translates to “cruelly hot day”.
The new term was designed to draw greater public attention to heat-related warnings, although it does not trigger any official measures nationwide.
At least six other spots saw 39.8 degrees heat on Wednesday.
Heatstroke alerts were in place across almost the whole country and emergency officials said on Wednesday that at least 14 of the almost 11,000 people who had sought sought emergency medical care in the past week had died from heat-related causes.
“Temperatures have been rising since mid-July, and severe heat is expected to continue nationwide,” the Fire and Disaster Management Agency said.
“It is no exaggeration to call this extreme heat a ‘disaster’ with many people being rushed to hospitals or even dying as a result of heatstroke.”
Japan sweltered through its hottest summer on record last year, with the highest recorded temperature registered on August 5, 2025, at 41.8 degrees in Isesaki, north of Tokyo. (AFP)
