A Chinese naval vessel firing flares at a Vietnamese fishing boat in the Hoang Sa (Paracel) Islands on March 20 is "dangerous and a disproportionate response," Carl Thayer, a maritime expert at the University of New South Wales in Australia, said.
He told Vietweek in an email: "This particular incident is worrying because it involved a naval ship.
"As long as the waters around the Paracel Islands remain in dispute, China should treat Vietnamese fishermen humanely," he said.
Tien Phong (Pioneer) newspaper quoted Bui Van Phai, 25, of Ly Son District, as saying that his boat encountered a Chinese vessel named 786 at around 10 a.m. on March 20 when it was winding up its fishing activities for the day.
The Chinese ship then gave chase for about 30 minutes, but he refused to stop.
The Chinese then fired flares at the boat. When its cabin caught fire as a result, the ship left the scene, Phai said.
The nine fishermen on board managed to put out the flames and prevent a potential explosion, he said
Earlier, on March 25, Ministry of Foreign Affairs spokesman Luong Thanh Nghi condemned China's act as "wrongful and inhumane" as the boat was fishing in traditional fishing grounds in Vietnam's Hoang Sa Archipelago.
"It is an extremely grave incident that violates Vietnam's sovereignty over Hoang Sa archipelago, endangers the lives of Vietnamese fishermen, and damages their properties," he said.
Chinese foreign ministry spokesman Hong Lei told reporters on March 26 that the action was "legitimate and necessary."
"According to verification with the relevant party, no damage was caused to the fishing boat from Vietnam," AFP quoted Lei as saying.
Later the same day the Chinese Defense Ministry said in a statement that sailors on board a navy vessel fired two flares at four Vietnamese boats, but denied Vietnam's claim that a vessel was damaged.
Thayer said the latest move by the Chinese is likely the consequence of establishing a military garrison in Sansha city and Hainan's new regulations concerning "illegal activities" in its Exclusive Economic Zone.
Vietnam has slammed China for a raft of activities it has undertaken to stake out its claims in the Sansha garrison, part of the Paracel Islands.
Though the population of Sansha city, known in English as Woody Island, is no more than a few thousand, mostly fishermen, its administrative responsibility covers China's vast claims in the East Sea and its myriad mostly uninhabited atolls and reefs.
The Vietnamese government has since January 25 also beefed up sea patrols to stop foreign vessels from violating Vietnamese waters.
The move followed China announcing rules that allow police in its southern island province of Hainan to board and seize control of foreign ships "illegally" entering what the country claims is its territorial waters in the East Sea.
Last November, China irked its neighbors by issuing six million new passports with a map showing almost all of the East Sea and disputed border areas as Chinese territory. Vietnam, the Philippines, and India have all refused to stamp the controversial passports.
Beijing claims virtually all of the East Sea, also known as the South China Sea, which includes both the Hoang Sa and Truong Sa (Spratly) islands.
The East Sea is thought to hold vast untapped reserves of oil and natural gas that could potentially place China, the Philippines, Vietnam, and other claimant nations alongside the likes of Saudi Arabia, Russia, and Qatar.
The waters hold around 11 billion barrels of oil and 190 trillion cubic feet of natural gas in proven and probable reserves, Reuters reported, citing the US Energy Information Administration.