With the monsoon season coming to an end, South Korea has seen a surge in the number of days with scorching heat, leading to a rapid increase in the number of cases of heat-related illnesses.

According to the Korea Disease Control and Prevention Agency on Friday, 507 medical institutions equipped with emergency rooms reported to the agency that they saw 124 patients with heat-related illnesses from Monday to Wednesday, 55 of which were from Wednesday alone.

The KDCA added that 16.3 percent of the total number of heat-related illnesses reported since it first started monitoring such cases this year came from the past three days. Since May 20, the agency has seen up to 759 cases of heat-related illnesses.

The number of cases this week was also 3.5 times higher than those last week, as the agency reported 35 heat-related illness cases from July 15 to 17.

So far, 78.7 percent of the patients with heat-related illnesses were male, with 29.5 percent of these patients being age 65 and up. Of the patients with heat-related illnesses, 11.1 percent and 13.2 percent were in their 20s and 30s, respectively.

By illness, heat exhaustion accounted for the largest share of cases or 54.4 percent, followed by heat stroke, heat cramps and heat syncope.

According to the KDCA, this week’s spike in the number of heat-related illnesses is likely due to the rise in temperatures and humidity levels caused by intermittent rain showers nationwide.

On Wednesday, Korea’s average daytime temperatures reached 34 degrees Celsius, with some cities in Gyeonggi Province, North Chungcheong Province and South Jeolla Province seeing temperatures reach 35 C.

Due to the high humidity levels, temperatures across most of Korea felt as intense as 35 C, prompting heat wave warnings to be issued nationwide from Wednesday lasting until Friday.

In Korea, heat wave warnings are activated when the highest apparent temperature is forecast to exceed 33 C for two consecutive days or more.

On Friday, the KMA raised the warning level from "caution" to "alert" in most parts of the country. Korea raises its heat wave warning level when daytime temperatures are forecast to exceed 35 C for two consecutive days or more.

The country's heat wave warnings have four levels of intensity: attention, caution, alert and serious.

Major cities like Seoul, Daejeon and Daegu expected to see daytime temperatures reach up to 34 C on Friday, with the capital city seeing the "alert" level warning for the first time this year.

In cities where a heat wave warning at the "alert" wasn't issued, a warning at the "caution" level remained.

The Korea Meteorological Administration noted that it might feel 1 to 2 degrees C hotter than the actual temperatures due to the increased humidity.

The KMA added that the recent high temperatures are due to layers of the atmosphere being covered with hot air.

"Currently, the upper layer of the atmosphere is covered by the hot and dry Tibetan anticyclone, while the mid and lower atmosphere is covered by the warm and humid North Pacific anticyclone,” said KMA official Woo Jin-kyu through an official statement issued to the press.

Woo added that Typhoon Gaemi, which made landfall in southeastern China on Thursday afternoon, will also “continue to bring hot, moist air into the region,” making the high temperatures and heat wave warnings persist over the weekend.