CHENGDU, China, May 24 (Reuters) - U.N. Secretary-General Ban Ki-moon arrived in quake-hit southwest China on Saturday to meet victims and witness the devastation first-hand, after visiting neighbouring Myanmar to see the aftermath of a massive cyclone.

The known death toll from the 7.9 magnitude quake already exceeds 55,000, but nearly 25,000 are missing and more bodies are expected to be found as the debris from flattened cities, towns and villages is cleared.

Beijing has largely won praise for its relief efforts, sending over 100,000 troops and a string of senior leaders to the worst-hit areas and accepting some foreign help even though the quake zone is home to China's chief nuclear weapons research lab.

In contrast, secretive Myanmar focused on holding a referendum even after Cyclone Nargis slammed into the country on May 2 and barred most foreign aid workers, even though the government appears ill-equipped to help the estimated 2.4 million destitute.

The storm and a sea surge it caused have already left nearly 134,000 dead or missing.

But after Ban's visit the military junta that rules the country agreed to admit foreign aid workers of all nationalities to the worst-hit delta area, in what the U.N. called a breakthrough for helping survivors.

In China, soldiers, relief workers and normal residents are already focused on reconstruction, although mountainous terrain means some places are still cut off after highways buckled, bridges collapsed and landslides blocked roads.

Ban, who requested the visit, will take a helicopter to the quake epicentre where he will meet the Prime Minister Wen Jiabao, who has been a driving force behind Chinese rescue efforts. (Reporting by Patrick Worsnip; writing by Emma Graham-Harrison; Editing by Bill Tarrant)

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