At least 600 people at the World Scout Jamboree, which kicked off in southwestern Buan on Tuesday, have so far been treated for heat-related ailments, officials said.
The event coincides with the highest level heat warning by the government in four years, as temperatures in some parts of the country exceeded 38 degrees Celsius (100.4 Fahrenheit) this week.
Yoon called for an "unlimited" supply of buses where the scouts can rest and cool down and trucks to provide water, his press secretary, Kim Eun-hye, said in a statement.
He also ordered officials to improve the quality of food being provided to the young people and all government agencies to join efforts to resolve any problems at the campsite.
More than 43,000 participants, most of them scouts aged between 14 and 18, are attending the jamboree, the first global gathering of the scouts since the pandemic.