By Manuel Mogato and Nguyen Phuong Linh

MANILA/HANOI (Reuters) - Vietnamese and Philippine troops got together on a disputed island in the South China Sea on Sunday to play soccer and volleyball - as well as drink beer - in a display of unity that will not go unnoticed in Beijing.

Philippine naval officials billed the event on the Vietnamese-held island as a chance to show the world there can be harmony in the South China Sea despite a web of overlapping claims to the potentially energy-rich waters.

The gathering on Southwest Cay in the Spratly archipelago also symbolises how once-suspicious neighbours are cooperating in the face of China's growing assertiveness in disputed waters.

About 40 Philippine naval personnel sailed to the island for the day-long event, Philippine naval officials said.

Coincidentally, the Philippines occupied Southwest Cay until early 1975, when troops from then South Vietnam seized it after Philippine forces sailed a couple of miles to Northeast Cay, which was under Manila's control, for a party.

The South Vietnamese were soon displaced by the communist forces of a victorious Hanoi.

Besides playing soccer and volleyball, the troops held a tug-of-war competition, put on cultural shows involving singing and dancing and shared food and beer, said Philippine naval spokesman, Lieutenant-Commander Gerard Fabic.

They also shared information on maritime security, natural disaster warnings and search and rescue operations.

Colonel Le Xuan Thuy, a Vietnamese naval official, said the event reflected the goodwill between the two countries.

He told troops from both sides that current conditions in the region were complicated by the "unruly actions of China seriously violating international laws".

The gathering underscores the growing cooperation between Hanoi and Manila - the two capitals most feeling China's wrath over the South China Sea - even though both still claim Southwest Cay and dispute other islands. Southwest Cay is almost equidistant from Vietnam and the Philippines.

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"We are not only bringing down walls of mistrust and suspicion with one another but building trust and confidence towards peacefully resolving our competing claims," said a senior Philippine naval official who declined to be identified.

The Philippines would hold a similar event next year, officials said.

CHINA DRIVING COUNTRIES TOGETHER

The Philippines, Malaysia and Brunei each claim some of the Spratlys, while China, Taiwan and Vietnam claim the whole chain.

China also claims 90 percent of the 3.5 million sq km (1.35 million sq mile) South China Sea, its reach displayed on its official maps with a so-called nine-dash line that extends deep into the maritime heart of Southeast Asia.

Beijing accuses the other claimants of stirring up trouble in the region.

Diplomats and experts have described the nascent partnership between Hanoi and Manila as part of a web of evolving relationships across Asia that are being driven by fear of China as well as doubts among some, especially in Japan, over the U.S. commitment to the region. [ID:nL4N0MV236]

They have said there were increasing levels of trust at a working level, as countries find that China's projection of naval power into Asia's waters is driving them together.

Most recently, Vietnam expressed interest in a legal case Manila filed at an international arbitration tribunal in late March, challenging China over its claims in the South China Sea.

Indeed, Vietnamese Prime Minister Nguyen Tan Dung said last month his government was considering taking legal action against China following the deployment of a Chinese oil rig to waters that Hanoi also claims. Vietnamese officials have not elaborated.

The Philippine and Vietnamese navies recently agreed to expand cooperation in disputed areas and a Vietnamese guided missile cruiser will soon visit Manila, Philippine naval officials have said.

(Writing by Dean Yates; Editing by Michael Perry)