Most of the country remained under heat advisories or warnings, while severe heat alerts were issued across parts of the southeastern Yeongnam region, including Changwon, Jinju, Gimhae, Yangsan, Pohang, Gyeongju and Gyeongsan, where the perceived temperature was forecast to exceed 38 C.
The Ministry of the Interior and Safety upgraded the national heat disaster warning to "serious," the highest of the four-tier crisis system, as extreme temperatures threatened public health, livestock and crops.
The heat wave has already taken a growing toll.
A Thai farm worker in his 30s collapsed and died while working in a field in Haenam, South Jeolla Province, on Friday in a suspected heat-related incident.
Health authorities reported a steady rise in heat-related illnesses across the country. South Jeolla and Gwangju had recorded 110 patients as of Friday, while South Gyeongsang reported 112 cumulative cases since mid-May. Chungcheong Province added four more heat exhaustion patients on Sunday, bringing its total to 84, including cases of heatstroke, heat cramps and heat syncope. Daegu has reported 45 heat-related illnesses since the first case this season in May.
The oppressive conditions have emptied streets, farms and even beaches during the hottest hours of the day, with many residents choosing to remain indoors under air conditioning. Others without access to cooling, particularly vulnerable elderly and low-income residents, have sought refuge in parks, shopping malls, banks and other public buildings with air conditioning.
Authorities also warned that the prolonged heat is beginning to strain livestock and agriculture.
As of Thursday, more than 10,500 animals had died from heat stress in South Gyeongsang Province alone, including about 2,500 pigs and more than 8,000 poultry. South Jeolla and Gwangju reported the deaths of over 16,000 livestock, while Chungcheong Province recorded nearly 24,000 losses. North Jeolla reported more than 60,000 livestock deaths, and North Chungcheong reported over 21,000.
Officials said poultry are particularly vulnerable because of dense farming conditions, while pigs have relatively poor natural ability to regulate body temperature.
The highest temperatures were recorded in the southeast.
Gyeongju registered 39.1 C on Monday afternoon, the highest official daytime temperature nationwide, while an automated weather station in Daegu's Sinam district measured 39.2 C. Heat indices exceeded 37 C in several locations, including Gyeongju, Goryeong and northern Daegu, approaching levels considered life-threatening for prolonged outdoor exposure.
The Korea Meteorological Administration considers a heat index of 38 C or an air temperature of 39 C sufficient to pose serious risks to human health and recommends suspending outdoor work and activities, taking frequent breaks and staying well hydrated.
Forecasters said the extreme heat is expected to persist for the time being, with widespread tropical nights likely to continue as temperatures remain unusually high even after sunset.
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