The World Bank subsequently froze its funding to Cambodia, pending more results in curbing land grabs.
Thailand and China want to boost annual bilateral trade to $100 billion by 2015.
Skyscrapers are Cambodia's new symbols of prosperity and modernity.
Around 1.8 million Cambodians took the occasion of the New Year to travel around the country this year.
The group rates Cambodia the 20th-most corrupt nation in the world, putting it in the company of Guinea, Kyrgyzstan and Yemen.
Hun Sen said claims on the South China Sea should remain a regional issue between “Asean and China only.”
Several Asean members, notably the Philippines and Vietnam, have overlapping claims to the sea with China and Taiwan.
China claims ownership of much of the South China Sea, along with four ASEAN states, including the Philippines.
Host President Hun Sen focused on economic issues in his opening remarks Tuesday.
Cambodia had left the contentious issue off the agenda, following a visit by Chinese President Hu Jiantao over the weekend.
The displaced at Phnom Bath say they are vulnerable to heavy winds and rainstorms, and they fear poisonous snakes and insects.