PYONGYANG (AFP) - North Korea wrapped up the 70th birthday party for its ruling Worker's Party on Sunday with a music and dance extravaganza that included a scene of children on a butterfly-collecting trip being killed in a US bombing raid.

With titular head of state Kim Yong-Nam as guest of honour, the open-air show - held on a floating stage on Pyongyang's Taedong river - was a chronological tribute to the party's role in shaping the country over the past seven decades.

It ticked every milestone as it went along - through liberation from Japanese rule and the Korean War, to the struggle of post-war reconstruction.

If the Workers' Party was the focus, the lion's share of credit went to founder leader Kim Il-Sung and his successor and son Kim Jong-Il, whose images were repeatedly projected on a giant screen to applause from the thousands of spectators gathered on the river bank.

It was a marathon event, which took more than two hours to reach the halfway mark, at which point a substantial number of people took advantage of a fireworks display to escape the wind and cold.

But many more stayed, especially those of the generation that grew up with the patriotic songbook that provided the concert's backbone.

And many of the performances were given by the original artists, some now in their 60s or late 70s.

The songs were interspersed with dramatic dance sequences, featuring guerrilla fighters, exhaustingly keen steel workers and, at one stage, a group of primary school children who ran on stage and acted an outing in the fields to collect butterflies.

The image on the screen above then shifted from fields of flowers to a squadron of US bombers dropping their payloads on the children below.

The concert was originally scheduled for Saturday evening, as the finale to a day of anniversary celebrations centred around a massive military parade in Pyongyang's Kim il-Sung square.

But torrential rain that came close to extinguishing a torchlight parade forced the event to be postponed until Sunday.