There were four deaths among the 4,138 people taken by ambulance to hospitals for heatstroke in the week through Sunday, the Fire and Disaster Management Agency said Tuesday in a preliminary report.
Of the total, 38.7 percent were 65 or older.
The hospitalization rate was 23 percent higher than the previous week's 3,361.
On Friday alone, 1,274 people were taken to hospitals when the temperature soared to 35 or higher in various parts of the country, according to the agency.