Vietnam accused a Chinese vessel of ramming and sinking a Vietnamese fishing boat in the disputed South China Sea.
The claim sharpened already dangerously high tensions between the two nations over their overlapping territorial claims in the waters.
The alleged incident occurred yesterday around 18 miles from a large oil rig that China deployed on May 1 in a disputed section of the sea, according to Tran Van Linh, president of the Fisheries Association in the central port city of Danang.
The rig deployment infuriated Hanoi and set off violent anti-China protests that further soured ties between the neighbouring communist countries with close economic relations.
Vietnam sent patrol ships to confront the rig, and China has deployed scores of vessels to protect it.
The two sides have been involved in a tense stand-off, occasionally colliding with each other.
“I call this an act of attempted murder because the Chinese sank a Vietnamese fishing boat and then ran away,” Mr Linh said.
“We vehemently protest this perverse, brutal and inhumane action by Chinese side.”
Chinese officials did not immediately comment.
China and Vietnam have long sparred over who owns what in the oil and gas-rich waters. Incidents between fishing crews are quite common, but Mr Linh said this was the first time China had sunk a Vietnamese boat.
He said about 40 Chinese steel vessels surrounded a group of smaller, wooden Vietnamese fishing ships yesterday Monday afternoon.
He said one then rammed into the Vietnamese ship, tossing 10 fishermen into the water and sinking the boat. The fishermen were picked by the other Vietnamese boats and there were no injuries.
The sunken fishing boat with its equipment and seafood catch was worth £142,000, and the association was demanding compensation, Mr Linh said.
Since May 1, Vietnam has accused China of ramming into or firing water cannons at Vietnamese vessels trying to get close to the rig, damaging several boats and injuring fisheries surveillance officers.
They have shown video footage of some of the incidents. China accuses Vietnam of doing the same.
China claims nearly all of the South China Sea as its own, bringing it into conflict with the far smaller nations of Vietnam, the Philippines and three others that have rival claims.
In recent years it has been more assertive in pressing its claims in the waters and resisting attempts to negotiate.
The US, which shares the concerns of the smaller claimant states about China’s rising military might, called China’s deployment of the rig “provocative”.
Vietnam is trying to rally regional and international support against Beijing, but its options are limited because China is the country’s largest trading partner.