BEIJING — Hair-trigger tensions in the South China Sea escalated Tuesday as China and Vietnam traded accusations over the sinking of a Vietnamese fishing vessel in the vicinity of a Chinese oil rig parked in disputed waters off Vietnam’s coast.
The incident was almost certain to aggravate the already charged diplomatic and economic tensions between China and Vietnam, whose relations have plummeted to the worst in decades following anti-Chinese riots two weeks ago that killed at least four people.
In the latest incident, a Chinese vessel rammed and sank a Vietnamese fishing boat about 17 nautical miles southwest of the rig on Monday afternoon, the state-run Vietnamese television network, VTV1, reported. All 10 crew members were rescued, the network said.
But Beijing labeled Vietnam as the aggressor, with the Chinese state-run news agency, Xinhua, saying the Vietnamese fishing boat “capsized when it was interfering with and ramming” a Chinese fishing vessel from Hainan, a province of China. Then China accused Vietnam of sabotage and interfering with the operations of the oil rig, which has become a flash point of tensions ever since Vietnam learned that the Chinese had set up the rig in waters contested by both nations.
Chinese and Vietnamese boats have rammed each other in the area around the oil rig, and the Chinese have acknowledged that they used water cannons to keep the Vietnamese away from the rig, which stands as tall as a 40-story building.
The rig arrived in the waters off the Paracel Islands, which are claimed by both China and Vietnam, on May 1, a unilateral move that showed China was willing to create “facts” establishing its control of the waters of the South China Sea without consulting with other claimants.
“Suddenly Chinese fishing boat #11209 crashed into Vietnamese fishing boat DNa 90152 with 10 fishermen on board,” the VTV1 television report said. A deputy colonel in the Vietnamese Coast Guard, Ngo Ngoc Thu, said the Chinese ship had a steel hull.
An armada of as many as 80 boats, including some from the Chinese Coast Guard, now patrol around the rig, creating a wide perimeter established by the Chinese, according to Vietnamese accounts.
Warships from both countries, including five Chinese frigates, have been observed from outside the perimeter, American officials say.
Chinese social media sites lit up Tuesday with nationalistic postings inspired by the placement of the oil rig and Monday’s clash at sea. Users of ifeng.com, the website of Phoenix Television, a Hong Kong-based satellite network, sent congratulations to the Chinese ship for its action in sinking the Vietnamese vessel.
“Now this is showing some backbone,” said one anonymous user. “Good going, finally seeing some news of concrete action,” said another.
And the depth of anti-Chinese sentiment in Vietnam was on stark display last Friday when a 67-year-old Vietnamese woman set herself on fire and died in Ho Chi Minh City, an echo of the self-immolations by Buddhist monks in South Vietnam in the early 1960s during the Vietnam War.
In the latest incident, the woman burned herself at dawn in the center of the city, and she left behind papers imploring the Vietnamese government to act more aggressively against the Chinese oil rig, city officials said.
The episode between the Chinese and Vietnamese fishing vessels came after anti-Chinese riots in Vietnam resulted in the deaths of four Chinese workers and injuries to more than 100. China evacuated several thousand workers from Vietnam last week.
A report by Xinhua on Tuesday cited CNOOC as saying that the rig had finished its first phase of operation and would stay in the area until mid-August. The Vietnamese Fisheries Resources Surveillance Department said the rig was moved about a few hundred feet north on Sunday, but the significance of the move was not immediately clear.
In a signal of how China, under the leadership of President Xi Jinping, now views the South China Sea as a top foreign policy priority, the country’s vice foreign minister said Tuesday that the sea was central to China’s very existence as a global economic power.
“Being the lifeline for China, the South China Sea is far more important to China than to other countries,” the minister, Liu Zhenmin, told reporters in Beijing.
China and Vietnam have enjoyed good relations between the Communist parties that run the two governments, and according to people close to the Vietnamese, the parking of the oil rig in disputed waters came as a surprise.
Since May 1, China has declined to hold substantive talks with Vietnam on the rig or the territorial claims in the South China Sea, a further indication of China’s resolve to make its claims unilaterally, Asian diplomats say. In response, Vietnam has threatened to take the matter to international arbitration, as the Philippines has already done.
The United States has urged restraint on both sides, and Adm. Samuel J. Locklear, the commander of the Pacific Fleet, warned last Friday that the proximity of the boats around the oil rig could lead to a collision.
It was initially impossible to determine whether the Chinese government controlled the Chinese fishing vessel involved in the clash, said Dennis J. Blasko, a former military attaché at the American embassy in Beijing. “We don’t know enough yet if this was coordinated or an individual action,” he said.
Many fishing boats are part of the Chinese militia, which are part of the Chinese armed forces, he said. “If the boat was part of the militia, it could have gotten an order fro the People’s Armed Forces Department,” he said.
The Chinese have publicly acknowledged that 80% of China’s fishing boats, including those operating out of Hainan, carry navigation equipment that is subsidized by the Chinese government.
The Beidou navigation satellite system, considered to be a Chinese version of GPS, allows the boats to send instant alarms and short messaging services, according to Qi Chengye, a manger of BDStar Navigation, which provides the Beidou system to Chinese vessels.
“The Chinese government is giving large subsidies to encourage fishermen to install BDS,” Mr. Qi said in an interview in Xinhua last year.