A crowd of visitors are spotted at Gyeongpo Beach in Gangneung, Gangwon Province, as the city's temperatures reached as high as 31 degrees Celsius on Sunday. (Yonhap)

South Korea sweltered through its first 40 degrees Celsius temperature in six years on Sunday, amid a relentless heatwave that has gripped the country since the end of July, following the monsoon season.

Current weather conditions on the Korean Peninsula are strikingly similar to those of the record-breaking summer of 2018, sparking concerns that this year could become one of the hottest on record.

The severe heatwave has already resulted in approximately 540 cases of heat-related illnesses from Monday to Saturday and has been linked to five fatalities over just two days, from Friday to Sunday.

In the city of Yeoju, Gyeonggi Province, the mercury hit 40 degrees Celsius at 3:33 p.m. on Sunday, marking the first time temperatures have surpassed this threshold since August 2019, according to the Korea Meteorological Administration on Sunday.

South Korea has now recorded temperatures exceeding 40 degrees Celsius on eight occasions, including the most recent instance. The first such extreme temperature was documented on August 1, 1942, with no similar occurrences until a notable resurgence in August 2019.

The current heatwave, fueled by the convergence of Tibetan and North Pacific high-pressure systems, mirrors the severe conditions of the 2018 summer. This intense heat is expected to persist until at least August 14, with high temperatures and humidity continuing to impact the nation.

Amid the ongoing heatwave, the Korea Disease Control and Prevention Agency reported a sharp increase in heat-related illnesses, with 154 new cases recorded on Saturday alone. From Monday through Friday, a total of 386 cases were reported across 507 emergency rooms nationwide.

Since the heat illness surveillance system began on May 20, there have been 1,546 reported cases and 11 deaths suspected to be heat-related as of Saturday. Notably, five of these fatalities occurred on Friday and Saturday, highlighting a recent surge in mortality.

On Saturday, an 87-year-old woman in Gwangju was found unconscious while farming and suffering from heatstroke. Also on Saturday, a 50-something-year-old woman was found unconscious while farming and suffering from a heatstroke in Changwon. They were both rushed to nearby hospitals but pronounced dead later that day.

Following the consistent surge in patients with heat-related illnesses and temperatures being above 35 C, the Interior Ministry has maintained its heat wave response level on “serious,” the highest within its four-tier system, since July 31.

Korea has also seen damage to livestock due to the extreme heat.

From June 11 to Aug. 1, nearly 257,483 livestock animals, including around 20,000 pigs and 230,000 poultry, died due to heat, according to data provided by the Ministry of Agriculture, Food and Rural Affairs.

Heatwave warnings have been in effect daily since the Korea Meteorological Administration announced the end of the monsoon season on July 27.

A heat wave warning at the “alert” level was issued nationwide as of 3 p.m. on Sunday, with apparent daytime temperatures reaching as high as 36 C. In Korea, heat wave warnings at the “alert” level are activated when the highest apparent temperature is forecast to exceed 35 C for two consecutive days or more.

Some cities, including Andong in North Gyeongsang Province, Gongju in South Chungcheong Province and Anseong in Gyeonggi Province reported real-feel temperatures as hot as 37 to 38 C.

Due to Sunday’s extreme temperatures, the Korea Baseball Organization announced that it would be canceling two of its baseball games scheduled to take place in Seoul and Ulsan at 5 p.m. on the same day. This is the second and third time that a professional baseball game has been canceled since the KBO enacted heat wave regulations in 2015.

Tropical night phenomena are also expected to continue, which refers to a phenomenon where the lowest temperature remains above 25 degrees Celsius between 6:01 p.m. the night before and 9 a.m. the next day. The country has also experienced a high number of tropical nights, with July seeing the highest number of tropical nights on record, according to the KMA.

As of Sunday, Seoul saw up to 14 consecutive tropical nights since July 21, while Gangneung in Gangwon Province and Jeju Island saw 16 and 19 consecutive tropical nights since July 19 and July 16, respectively. The state weather agency anticipates more tropical nights to be observed for the next few days, due to the expected persistent heat waves.