The number of people who died this year due to heat-related illnesses has reached 18 amid the prolonged heat wave across the country. 

According to the Korea Disease Control and Prevention Agency on Monday, it is the highest heat-related death toll to be posted in three years. The figure was also the second highest to be posted since July 2011 when the government began to compile such data. 

The agency said the number of people treated for such diseases at hospital emergency rooms around the country reached one-thousand-212 between May 20 and last Saturday. That’s more than two-point-five times larger compared to the same period last year. 

Heat stroke was the cause of death for all 18 who died this year, with most of the deceased being in their 50s. 

The agency cited that the nation saw heat-related deaths for the past four consecutive weeks.