Saturday’s pullout by the US is a fresh blow to the organisers and the South Korean government, which on Friday promised more water trucks, air-conditioned spaces and medics in an attempt to save the event.

Temperatures have hit 34 Celsius in Saemangeum, near the city of Buan on South Korea’s west coast, where 39,000 participants, mostly scouts aged 14-18, were camping as of Friday.

The US contingent will take part in a jamboree programme on Saturday before moving to US Army Garrison Humphreys near the jamboree site on Sunday, according to an email reviewed by Reuters.

“The US Contingent to the World Scout Jamboree has made the difficult decision that we will be departing the 25th World Scout Jamboree site early because of ongoing extreme weather and resulting conditions at the jamboree site,” said the email sent to parents by the US group’s media team.

Britain, the largest grouping at the jamboree, said on Friday they were moving to hotels in Seoul for the rest of their stay, to alleviate pressure on the site.

British scouts were seen leaving the campsite with their bags in Buan on Saturday morning, according to a Reuters witness.

The World Organization of the Scout Movement said in a statement on Friday it had asked the Korean Scout Association to consider “alternative options to end the event earlier than scheduled and support the participants until they depart for their home countries.”

Organisers would meet on Saturday to discuss whether to continue, cancel or scale back the event, South Korea’s Yonhap news agency reported.

Hit by extreme heat, hundreds of participants at the event fell ill and were treated for heat-related ailments, prompting complaints from parents over the safety of their children.

More than 150 countries were taking part in the gathering as of Friday, according to officials.

The jamboree is scheduled to run until Aug 12.