The science ministry issued a heatwave warning in most parts of the nation on Saturday.
Temperatures will hover between 28 to 36 degrees celsius.
In the early hours of the day in the west and east sea and Jeju's coastal areas, thick fog is expected, so drivers are advised to take caution.
Some rain is forecast in the mountainous regions as well.
People are advised to remain hydrated and refrain from excessive consumption of caffeine and alcohol.
Outdoor activities during the daytime should be avoided if possible.
Those who need to be outside are advised to take breaks and find shade as often as possible.