The brown-stained bones -- including some near-complete skulls -- were laid out on tables at the temporary ossuary in Incheon before being placed in identical boxes pending their repatriation Wednesday.

It will be the fifth annual return under a 2013 agreement which has so far seen 569 sets of remains sent back.

Communist Chinese forces played a crucial role in support of the North during the 1950-53 Korean War, but former South Korean president Park Geun-hye offered to return the bodies of Beijing's war dead as a goodwill gesture.

Mao Zedong sent millions of troops to intervene as US-led United Nations forces drove Kim Il Sung's army back towards the Chinese frontier in late 1950, saving the North from defeat in a decisive turning point in the war.

South Korean and UN forces were pushed back south, losing control of Seoul before recovering to recapture the capital and end up in a stalemate along what is now the Demilitarized Zone.

Casualty figures remain disputed but Western estimates commonly cite a figure of 400,000 Chinese deaths, while Chinese sources mention a death toll of about 180,000.

The repatriations take place ahead of China's annual Qingming -- tomb-sweeping -- festival, when many people visit and clean the graves of their ancestors.

The bodies being sent back Wednesday were exhumed last year from multiple sites in Gangwon province in South Korea's northeast, a defence ministry spokesman told AFP.

Hundreds of North Korean soldiers remain interred at a special cemetery plot in Paju, just south of the heavily fortified border with North Korea, but Pyongyang has ignored Seoul's offers to return them despite sporadic talks on the issue.