South Korean rapper Psy will give a free concert in Seoul Thursday, capping a stunning month in which his hit "Gangnam Style" has stormed global charts and made the chubby 34-year-old a national hero.

Around 50,000 fans were expected to turn out for the show in front of the capital's City Hall that will be streamed live to an international audience via YouTube -- the forum that launched him to stardom in the first place.

The video to "Gangnam Style", featuring Psy's much-imitated horse-riding dance, went viral after its July release on the Google-owned video sharing site, where it has now notched up more than 350 million views.

Almost overnight, Psy was transformed into South Korea's best-known cultural export, succeeding where the manufactured girl and boy bands of the homegrown "K-pop" phenomenon have failed by breaking into the US market.

Despite being sung almost entirely in Korean, the song is currently top of the British charts and number two on the US Billboard's Hot 100 chart.

During a hugely successful US promotional tour last month, Psy made a guest appearance at the MTV awards in Los Angeles, taught his signature dance to Britney Spears, and was given a cameo role on NBC's "Saturday Night Live."

His horse-riding moves have been imitated, parodied and referenced in pretty much every conceivable context.

Jay Leno's "Tonight Show" produced a mock-up video showing US presidential candidate Mitt Romney doing the dance at the Republican convention, while West Indian batsman Chris Gayle has adopted it for his celebrations at the ongoing T20 cricket World Cup.

Even Stalinist North Korea has jumped on the bandwagon, posting a "Gangnam Style" parody on its official government website that mocks Park Geun-Hye, the conservative front-running candidate in South Korea's presidential election.

The Gangnam of the title is Seoul's wealthiest residential and shopping district, lined with luxury boutiques, top-end bars and restaurants frequented by celebrities and well-heeled, designer-clad socialites.

The video pokes fun at the district's lifestyle, with Psy cavorting through a world of speedboats, yoga classes and exclusive clubs.

Psy, whose real name is Park Jae-Sang, is a product of Gangnam, having been born in the district to affluent parents. He later attended the Berklee College of Music in Boston.

A relative veteran after more than a decade on the Korean music scene, Psy had previously built up a small but loyal fan base that stuck with him through numerous ups and downs, including an early brush with the law for smoking marijuana.

In 2007, he was forced to serve a second period of compulsory military service after it was revealed he had continued with his showbiz interests during his first two-year stint.

"This is my heyday, in 12 years since I debuted as a singer... this is just unbelievable, and I'm thankful for everything," Psy told a press conference in Seoul after his triumphant return from the US.

While some articles in the western media have suggested Psy's overseas popularity may be linked to negative Asian stereotyping, the overwhelming domestic response to his success has been one of national pride.

The South Korean government sees popular culture as a potent export force that provides national branding for a country that still feels overlooked internationally compared to neighbours China and Japan.

The government expended much time and money supporting the so-called Hallyu (Korean Wave) of TV shows and pop music that swept across Asia in the past decade.

Thursday's free concert is being co-organised by the Seoul municipal authorities, who have promised to extend subway services and block off traffic from the area around the city centre venue.

"He's the best live performer in the country," said student Kim Ju-Won, 22, adding he was unsurprised by Psy's spectacular success.

"Languages are different, but people around the world have the same emotions... and Psy is full of emotion and energy," said Kim, who arrived at the concert venue eight hours early to secure a vantage point.