People play at a water park in Busan, Monday, as a severe heat wave warning is in effect. Yonhap

The state weather service issued its highest-level heat wave warning for 17 areas in southern Korea on Monday, saying extreme heat is expected there.

The serious heat wave warning had been issued as of 11 a.m. in Daegu, nine South Gyeongsang Province areas, including Gimhae, Miryang, Yangsan, Uiryeong, Jinju and Changwon; six North Gyeongsang Province areas, including Gyeongsan, Pohang and Gyeongju, and Gwangyang of South Jeolla Province, according to the Korea Meteorological Administration (KMA).

The serious heat wave warning is the highest warning level established 18 years after the heat wave advisory system was introduced in 2008.

It is issued when the highest perceived temperature reaches 38 C or higher, or the maximum daily temperature reaches 39 C or higher, levels considered life-threatening.