A record 628 people suffering heat exhaustion and heatstroke had to be taken to Tokyo hospitals by ambulance in July, the Tokyo Fire Department said Sunday.
The tally was the highest since 1999, when the department started taking the statistics. The previous record was 538 in July 2001.
The figure was up sharply from 14 in July of last year, which had an unusually cool summer.
This year, the mercury hit an all-time high for Tokyo of 39.5 degrees July 20.
Of the 628 people hospitalized, 418 were men and 210 were women. Though there were no fatalities, 70 were listed as seriously ill, unconscious or in critical condition.
Of those 70 people, 42 developed heat exhaustion indoors.
Reflecting the aging society, many people who became sick indoors were in their 60s through 90s. There were cases of elderly living alone and being found ill by family members or social workers, according to the department.
"It's important to lower one's body temperature by drinking liquids," a department official said.