South Korea issued its first-ever emergency heatwave alert on Sunday under a new warning system launched this year, advising people to halt outdoor activities and keep cool.
The new warning system was introduced to better deal with a rising number of heatwaves in South Korea, which have become longer and more intense, officials said.
An emergency alert is issued when areas experiencing a heatwave are forecast to hit perceived temperatures of 38C or an actual temperature of 39C for one day.
"The Korea Meteorological Administration issued an Emergency Heatwave Warning at 10 am today (GMT 0100) for two cities in southern North Gyeongsang Province -- Gyeongsan and Pohang," said agency chief Lee Mi-seon at a press briefing.
"This marks the first time it has been issued since the system took effect," she added, according to AFP.
The affected areas saw temperatures reach the emergency criteria over the weekend.
"An emergency heatwave warning does not simply mean the weather is extremely hot," Lee said.
"It indicates conditions in which even healthy people face a significantly elevated risk of serious harm, including heat-related illness and death."
People engaged in outdoor activities should stop immediately and move to a cool place, and no one, including children or pets, should be left inside a vehicle, she added.
Much of the country -- including parts of Seoul -- remained under heatwave warnings, which are issued when the perceived temperature is expected to stay at 35C or higher for two consecutive days.
Such warnings take both temperature and humidity into account, according to the KMA.
Children tried to cool off from the heat on Sunday by running through the water jets at Gwanghwamun Square in central Seoul, an AFP reporter saw.
People also sought refuge in air-conditioned shopping malls.
KMA data show the average annual number of heatwave days in the country has more than doubled to 19 over the past five years, from eight in the 1970s.
The average annual number of tropical nights has also jumped from four to 14 over the same period.
A heatwave day is defined as one with a maximum temperature of at least 33C, while a tropical night is one when the overnight low remains 25C or above.
The new system comes as Europe endures a scorching summer, after a June heatwave shattered temperature records across the continent.
Scientists warn that extreme weather events such as heatwaves are becoming more frequent and intense as a result of human-induced climate change.
