Vietnam said on Wednesday a Chinese vessel intentionally rammed two of its ships in a part of the disputed South China Sea where Beijing has deployed a giant oil rig, sending tensions spiraling in the region.
The Foreign Ministry in Hanoi said the collisions took place on Sunday and caused considerable damage to the Vietnamese ships. Six people suffered minor injuries, it said.
"On May 4, Chinese ships intentionally rammed two Vietnamese Sea Guard vessels," said Tran Duy Hai, a Foreign Ministry official and deputy head of Vietnam's national border committee.
"Chinese ships, with air support, sought to intimidate Vietnamese vessels. Water cannon was used," he told a news conference in Hanoi. Six other ships were also hit, but not as badly, other officials said.
Dozens of navy and coastguard vessels from both countries are in the area where China has deployed the giant rig, Vietnamese officials have said.
"No shots have been fired yet," said a Vietnamese navy official, who could not be identified because he was not authorized to speak to media. "Vietnam won't fire unless China fires first."
The two Communist nations have been trying to put aside border disputes and memories of a brief border war in 1979. Vietnam is usually careful about comments against China, with which it had bilateral trade surpassing $50 billion in 2013.
Still, Hanoi has strongly condemned the operation of the drilling rig in what it says are its waters in the South China Sea, and told the owners, China's state-run oil company CNOOC, to remove it.
The United States has also criticized the move.
The row comes days after U.S. President Barack Obama visited Asia to underline his commitment to allies including Japan and the Philippines, both locked in territorial disputes with China. Obama, promoting a strategic "pivot" towards the Asia-Pacific, also visited South Korea and Malaysia, but not China.
The United States is "strongly concerned about dangerous conduct and intimidation by vessels in the disputed area," U.S. State Department spokeswoman Jen Psaki said in Washington on Wednesday. Psaki reiterated the U.S. view that China's deployment of an oil rig was "provocative and unhelpful" to regional security.