Temperatures soared across the country on Wednesday with highs for this summer recorded in many areas, the weather agency said.
The Meteorological Agency issued heat wave advisories in more than 16 prefectures, warning of dehydration and encouraging the use of air conditioning.
Several hundred observation points nationwide recorded temperatures of 30 Celsius or higher, with the day's high of 35.9 Celsius reported in the cities of Higashiomi, Shiga Prefecture, and Niihama, Ehime Prefecture. Highs for the summer were logged at about 100 observation points.
The central business district of Tokyo recorded 33.1 Celsius shortly after 10 a.m.
The agency forecasts that the heat wave will last into the coming week as a high pressure system is likely to continue covering eastern and western parts of the country.
On Wednesday, the Fire and Disaster Management Agency announced that three people had died and more than 3,000 were taken by ambulance to hospital due to heatstroke or heat exhaustion last week.
A total of 3,179 people were taken to hospitals, up 29 percent from 2,473 the previous week, the agency said.
Some 1,096 patients had to be hospitalized, the agency said, and more than 40 percent of those taken to hospitals were 65 or older.
By region, Osaka had the most with 283 people transported last week to hospital, followed by Aichi with 272 and Tokyo with 236, the agency said.
Temperatures around Japan have been high as the rainy season draws to the close. The Meteorological Agency announced Tuesday the rainy season in the Kanto area had ended.