Vietnam's state-run media says one of the country's patrol ships has exchanged water cannon fire with Chinese vessels in an escalating dispute over Beijing's placement of an oil rig in disputed waters of the South China Sea.
The reports say the two sides shot high pressured water at each other Monday near the site of the oil rig, there were no reports of casualties.
At the just-concluded ASEAN summit in Burma, Vietnamese Prime Minister Nguyen Tan Dung accused Beijing of "extremely dangerous action" and called for the bloc to take a united stand on the issue.
ASEAN expressed "serious concern" over the situation and called for a peaceful resolution, but it did not mention China by name.
Monday, Chinese Foreign Ministry spokeswoman Hua Chunying said Hanoi's efforts to rally ASEAN against Beijing are bound to fail.
"The facts prove that Vietnam's attempt to rope in other parties and put pressure on China will not succeed," she said. "We hope that Vietnam can see the situation clearly, calmly face up to reality, and stop harassing Chinese operations."
Su Hao, director of the Center for Strategic and Conflict Management at China Foreign Affairs University, said Hanoi is the one trying to change the status quo, not Beijing.
"The problem at the moment is the Vietnamese have not accepted Chinese ad hoc control over the Paracel Islands. That's a problem. I do think that the Vietnamese should take a realistic attitude to accept the reality of China's [control] over the Paracel Islands," said Su.
Last week, Hanoi accused Chinese ships of intentionally ramming its vessels and blasting them with water cannons, injuring six Vietnamese sailors. This is the first time Vietnam has said its own ships also fired water cannons at the Chinese.
Tran Truong Thuy, director of the Center for SCS Studies, Diplomatic Academy of Vietnam, told VOA's Vietnamese service the tensions are an opportunity for expanded U.S.-Vietnam relations, but he said he does not expect a military alliance between the two.
"The South China Sea is where both nations share so many common interests, especially freedom of navigation and regional peace and stability. Both Vietnam and the U.S. are concerned about whether an arising China is a threat and if they are indeed developing peacefully. Those common concerns will accelerate Vietnam-U.S. relations."
In Washington on Monday, U.S. Secretary of State John Kerry said the United States and other nations are deeply concerned about what he called "aggressive" Chinese action in the South China Sea. Kerry said the dispute should be resolved peacefully through arbitration, but not confrontation.
China claims nearly the entire South China Sea. Its claims overlap with that of ASEAN members Vietnam, Brunei, Malaysia and the Philippines.