There were 21 deaths attributed to heat-related illnesses from May 20 to the end of July. Additionally, two more deaths were reported on Tuesday, Seoul-based Yonhap News reported.
Authorities have raised the heat wave alert to "serious," the highest level in the four-stage warning system.
Since mid-June, the South-Asian nation has been experiencing extremely hot weather due to the onset of the season's first heat wave alerts.
Temperatures have soared to approximately 35 degrees Celsius (95 degrees Fahrenheit) in many regions across the country.
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