Hundreds of participants at the 25th World Scout Jamboree in Buan, South Korea have been hit by heat exhaustion.
Some 400 cases were reported on the first night of the event on Tuesday, with many treated at a makeshift hospital at the campsite.
Temperatures have hit 35C (95F) in North Jeolla province, where the event is being held, amid a heatwave warning.
Scouts from the US, Bangladesh and the UK have been affected, local media is reporting.
The UK contingent is expected to be the largest in South Korea, numbering about 4,500 of the total 43,000 in attendance.
The UK Foreign Office said the situation was being closely monitored.
“Consular officials are on site to support attendees as planned and in line with standard practice for such events,” a spokesperson for the Foreign Office added.
“We are in regular contact with both Scouts UK and the relevant Korean authorities to ensure the safety of British nationals.”
Scouts UK has been approached for comment.
A fire service official told Reuters that most of the scouts who required medical attention experienced mild symptoms such as headaches, dizziness and nausea.
The official added that most have since returned to their campsites.
The jamboree, sometimes called the world’s largest youth camp, kicked off on Tuesday.