American and British scouts have pulled out of the World Scout Jamboree in South Korea citing scorching temperatures, as organisers weighed whether to cut short an event also reportedly plagued by dire campsite conditions.

About 43,000 people have joined the jamboree in North Jeolla province, but an extreme heatwave has seen hundreds of scouts fall ill, forcing Seoul to deploy military doctors and vow an all-out effort to salvage the event.

But despite the government's promises of air-conditioned buses and freezer trucks, the US contingent said on Saturday they would withdraw, following a British decision to exit on Friday, citing concerns over the extreme weather.

The American scouts will go to Camp Humphreys, a US Army garrison in Pyeongtaek, according to US officials.

The World Organization of the Scout Movement has called on South Korea to shorten the event — scheduled to run until August 12 in the coastal town of Buan — pointing to issues caused by one of the country's hottest summers in years.

The statement added that the South Korean government planned to stick to the schedule, "assuring that they will do everything possible to address the issues caused by the heatwave".

Singaporean scouts also decided to leave the site earlier than planned, and Belgian authorities were looking for accommodation elsewhere for their contingent, according to South Korea's Yonhap news agency.

Representatives from all participating countries are meeting on Saturday to decide how to proceed, officials told AFP news agency.

Poor campsite conditions

South Korea this week issued its highest hot weather advisory for the first time in four years.

On Friday, temperatures across the country ranged from 35 to 38 degrees Celsius. Scouts from the United Kingdom — the largest group at around 4,000 — said they were leaving late.

But reports in local media have suggested the event's issues go beyond the heat, citing poor campsite conditions, with sanitation "less than ideal" including rudimentary showers and toilets, and saying scouts had been plagued by insect bites.

A Korean-American parent, whose 15-year-old daughter lost consciousness while participating in the event, claimed an ambulance was called but it did not arrive at the site until 45 minutes later.

"We were told she lost consciousness and (her eyes rolled back), revealing the whites," she told South Korean broadcaster SBS.

"Those 45 minutes were terrifying for us. We can't even imagine what might have happened during that time. How can South Korea allow children to be neglected like this?"

The exit of British, American and other scout troops is a significant PR setback for the South Korean government, which on Friday called an emergency cabinet meeting and mobilised aid.