Vietnam has lodged an official protest with China following the sinking of a Vietnamese fishing vessel in the contested South China Sea , the foreign ministry said late on Thursday. The two countries have long been embroiled in a dispute over the potentially energy-rich stretch of waters, called the East Sea by Vietnam . The fishing vessel was moored near Da Loi island in the Paracel archipelago on March 6 when a China Maritime Surveillance Vessel chased it and fired a water cannon at it, the ministry said in a statement. The boat sank after hitting rocks while it was being chased. All five fishermen on board were rescued by another Vietnamese fishing boat, the ministry said. A Vietnamese rescue agency said earlier that the Chinese vessel rammed the fishing boat. “The Chinese vessel committed an act that violated Vietnam’s sovereignty over the Hoang Sa archipelago, threatened the lives and damaged the properties and the legitimate interests of Vietnamese fishermen,” the ministry said, referring to the Paracel Islands by their Vietnamese name. Vietnam had lodged a protest with China’s embassy in Hanoi and demanded that China deal strictly with its Maritime Surveillance agency to prevent similar incidents and to compensate fairly the fishermen for their losses. Vietnam frustrated by slow pace of talks on South China Sea code of conduct A Chinese foreign ministry spokesman in Beijing was cited by Chinese media as saying earlier that the fishing boat had sunk when the Chinese vessel approached, and that the Chinese crew had rescued the fishermen. China claims 90 per cent of the South China Sea, where it has steadily expanded military and other installations on artificial islands and reefs, unnerving the region and angering Washington. In addition to Vietnam, the Philippines, Malaysia, Brunei and Taiwan also have claims to parts of the sea.