In this May 7, 2012 file photo released by China's Xinhua News Agency, CNOOC 981, the first deep-water drilling rig developed in China, is pictured at 320 kilometers (200 miles) southeast of Hong Kong in the South China Sea

Vietnamese naval vessels and Chinese ships collided on Wednesday, a Vietnamese government official said, as Hanoi sought to prevent a Chinese oil rig from setting up in a disputed part of the South China Sea.The official said no ammunition had been fired and there were no reports for injuries as a result of the standoff, the most serious in years between the two countries in the sea. If neither side step downs, some analysts said they feared full blown skirmishes could break out between the two navies in what has long been regarded as a possible global flashpoint.China's stationing of the oil rig over the weekend has been seen as one of its most provocative steps in a gradual campaign of asserting its sovereignty in the South China Sea, parts of which are also claimed by Vietnam, the Philippines and other smaller Southeast Asian nations.Two foreign diplomats said Vietnam dispatched up to 29 armed naval and coast guard ships to areas near the oil rig when it became aware of China's intentions. Citing a Chinese diplomat, one said that the Vietnamese deployment was meant to be a "show of force" to get Beijing to withdraw the rig.All spoke on condition of anonymity because of the sensitivity of the information.China moved the giant deep-sea rig to an area close to the Paracel Islands on May 2, drawing angry protests from Vietnam.China seized control of the Paracels in 1974, but Vietnam has always claimed them - and the waters around them - as its own.The Vietnamese official said the Vietnamese flotilla was outnumbered by the size of a Chinese one sent to escort the rig.He said the ships were trying to stop the rig from "establishing a fixed position" in the spot where it wanted to drill.Beijing had previously announced that no foreign vessels would be allowed within a 3-mile (4.8-kilometer) radius of the rig, which it says is in its waters.China's assertiveness along with its growing military and economic might is alarming many in the region.The United States, which is undertaking a military and economic "pivot' toward Asia in part to counter Chinese influence, shares the concerns of the smaller nations. In a strongly worded statement in Washington on Tuesday, State Department spokeswoman Jen Psaki called China's action "provocative and unhelpful to the maintenance of peace and stability in the region."Vietnam has limited leverage in dealing with its giant neighbor and vital economic partner. It can't afford damaged ties with Beijing, and has no hope of competing with it militarily. But it also needs to show a strong response to appease domestic critics, who accuse it of being soft on China.

China occupied the Paracel islands 40 years ago, and 74 U.S.-backed South Vietnamese forces died in a subsequent military clash.The Vietnamese and Chinese navies clashed again in 1988 in the disputed Spratly Islands, leaving 64 Vietnamese sailors dead.