Tens of thousands of scouts danced, sang and waved glow sticks at a massive K-pop festival in Seoul on Friday, as South Korea sought to salvage a problem-plagued jamboree with "the power of Korean culture".

The quadrennial world jamboree gathered 43,000 scouts in North Jeolla province, but an unprecedented heatwave prompted mass illnesses, US and UK contingents left early amid reports of dire campsite conditions, and a tropical storm finally forced a full evacuation this week.

The scouts were dispersed across the country and sent on government-sponsored cultural tours, but the "K-pop Superlive" concert -- featuring major acts including NewJeans and The Boyz -- reunited all the jamboree participants for a grand finale.

Tens of thousands of scouts in colourful uniforms and neckties, some wearing face paint and waving flags, filled Seoul's World Cup Stadium Friday.

"The last few days have not been easy," said Ahmad Alhendawi, secretary-general of the World Organization of the Scout Movement, at the official closing ceremony ahead of the concert, adding to loud cheers that they had finally "reunited our jamboree".

Prime Minister Han Duck-soo told the scouts that he hoped "the cultural experiences you had in various parts of Korea... will remain as beautiful memories for you".

K-pop groups including HolyBang, The Boyz, ATBO and The New Six -- the latter wearing scout-themed costumes -- then performed to rapturous applause from the mostly teenage scouts.

The scouts, many wearing colourful raincoats, could be seen singing along, dancing and enthusiastically waving glow sticks.

Some used their smartphones to capture the faces of the K-pop stars, with many celebrating wildly when the cameras zoomed in on their faces, projecting them on the big screen.

Traffic control in Sangam-dong, the district where the stadium is located in Seoul, began hours before the concert, resulting in serious congestion in the area. More than 1,000 buses carried scouts to the venue.

Seoul's culture ministry said all scouts were given photo cards of BTS as a gift, provided for free by the septet's agency, HYBE. The photo cards were said to have a total retail value of 800 million won ($600,000), according to local media.

- 'Totalitarian idea' -

But even as the government throws millions of dollars in emergency funding into fixing an event that has been a public relations disaster, criticism -- from K-pop fans to public sector employees -- is mounting over Seoul's approach.

A popular TV music program, set to feature some acts now performing at the jamboree, was abruptly cancelled for undisclosed reasons.

And lawmaker Sung Il-jong faced backlash from K-pop fans after saying the army should let megastars BTS -- on hiatus while two members serve their mandatory military terms -- reunite and perform.

K-pop columnist Isak Choi said on the social media platform X that the plan betrayed "a terrible totalitarian idea that the state owns K-pop".

The Yonhap News Agency reported that around 1,000 employees at public institutions -- such as the Korea Development Bank and the Korea Electric Power Corporation -- had been "mobilised" to help out with the concert.

"Although the words used are 'request for cooperation', it's almost at the level of forced conscription during wartime," the Korean Financial Industry Union said in an angry response.

The venue is also proving controversial, as its wildly expensive "hybrid grass", ideal for sporting events, will be damaged by the concert stage.

"Idol fans are shedding tears as their favourites are being pulled out at the last minute. Football fans are also shedding tears as the expensive grass in the stadium is getting destroyed," one disgruntled person wrote on X in Korean.

"Who exactly benefits from this Jamboree concert?"