The affected areas saw temperatures reach the emergency criteria over the weekend.
“An emergency heatwave warning does not simply mean the weather is extremely hot,” Lee said.
“It indicates conditions in which even healthy people face a significantly elevated risk of serious harm, including heat-related illness and death.”
People engaged in outdoor activities should stop immediately and move to a cool place, and no one, including children or pets, should be left inside a vehicle, she added.
Much of the country – including parts of Seoul – remained under heatwave warnings, which are issued when the perceived temperature is expected to stay at 35°C or higher for two consecutive days.
Such warnings take both temperature and humidity into account, according to the KMA.
LONGER HEATWAVES
Children tried to cool off from the heat on Sunday by running through the water jets at Gwanghwamun Square in central Seoul, an AFP reporter saw.
People also sought refuge in air-conditioned shopping malls.
KMA data shows that the average annual number of heatwave days in the country has more than doubled to 19 over the past five years, from eight in the 1970s.
The average annual number of tropical nights has also jumped from four to 14 over the same period.
A heatwave day is defined as one with a maximum temperature of at least 33°C, while a tropical night is one when the overnight low remains 25°C or above.