TOKYO -- Vietnamese and Chinese ships collided Wednesday near a Chinese oil rig in waters claimed by both nations in the South China Sea, further escalating a rift that began when China began drilling near a disputed island group last weekend.
A Vietnamese official told The Associated Press that no ammunition was fired and there were no reports of injuries as a result of the standoff in waters near the Paracel Islands, about 150 miles from the Vietnamese coast and about 225 miles from China's Hainan Island.
China has held de facto control over the islands since a naval battle with South Vietnam in 1974, but Vietnam maintains its claim.
Two foreign diplomats told AP that 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.
The Vietnamese official said the flotilla was outnumbered by the size of a Chinese fleet escorting the rig, according to AP.
AP reported that all officials spoke on condition of anonymity because of the sensitivity of the information.
Chinese claims to roughly 90 percent of the South China Sea -- despite competing claims from Malaysia, Vietnam, the Philippines, Indonesia, Brunei and Taiwan -- have increasingly concerned security officials in the United States and elsewhere, largely because of their potential to spark conflict in an area where much of the world's energy resources and consumer goods travel on ships.
The United States also operates ships in the region in a bid to preserve freedom of navigation in international waters -- a concept China views far differently than the U.S. and many of its neighbors. While most nations claim rights to operations in the Exclusive Economic Zones within 200 nautical miles of a nation's shores, China does not.
Prior to reports of the collision, Daniel Russel, Assistant U.S. Secretary of State for East Asian and Pacific Affairs, said Wednesday that the United States was watching the conflict, but urged caution from all sides.
"We believe that it is critically important for each of the claimant countries to exercise care and restraint," he told Reuters during a visit to Hong Kong, ahead of a previously scheduled trip to Hanoi on Wednesday.
"The global economy is too fragile and regional stability is too important to be put at risk over short-term economic advantage."
The Maritime Safety Administration of China announced May 3 on its website that all ships should stay away from the rig, called the Haiyang Shiyou 981.
The decision drew immediate condemnation from Vietnam, where a foreign ministry spokesman called the area "undeniably within Vietnam's exclusive economic zone and continental shelf."
International maritime law generally considers waters within 200 nautical miles (230 statute miles) of a country's borders to be part of its exclusive economic zone.
China maintains it owns the area largely through a claim of historical discovery.
"Relevant drilling work is totally within waters off China's Xisha islands," said Chinese foreign ministry spokeswoman Hua Chunying, using a Chinese name for the Paracels, when asked about the escalating situation by reporters on May 6. Hua declined to elaborate.
China's move comes just after President Barack Obama's visit to Japan, South Korea, the Philippines and Malaysia. All except South Korea have territorial disputes with China.
During a news conference in Manila, Obama noted that the United States doesn't "go around sending ships and threatening folks" when it has territorial disputes, a pointed reference to China's actions.
In Washington on May 6, State Department officials criticized China's oil drilling in the area.
"Given the recent history of tensions in the South China Sea, China's decision to operate its oil rig in disputed waters is provocative and unhelpful to the maintenance of peace and stability in the region," State Department spokeswoman Jen Psaki said. "These events point to the need for claimants to clarify their claims in accordance with international law and reach agreement about what types of activities should be permissible within disputed areas."
China and Vietnam have repeatedly clashed over territory since Vietnam's official reunification in 1976. The two nations engaged in repeated border skirmishes from 1979 through 1990.
Besides the Paracel battle in 1974, the two navies fought over Johnson South Reef in the disputed Spratly Islands in 1988.
More than 70 Vietnamese sailors died in the Chinese victory, according to media reports.
Since then, China's military has grown far larger, as have its national ambitions for control of the South China Sea.
China has stepped up maritime patrols and flights over islands it considers its own based on historical discovery, but that at least six other nations also claim under international law.
U.S. allies and other nations in the region have accused Chinese ships of cutting their communications cables and restricting their ships' movements.
Last year, China imposed fishing regulations on large parts of the South China Sea that the Philippines, Malaysia, Vietnam and other nations either view as their own, or as international waters.
In recent years, Navy officials have accused Chinese ships of shadowing and obstructing the navigation of U.S. ships, though such accusations have dropped within the past year.