THE Marine Department is to investigate the sinking of a Hongkong fishing vessel in international waters after a collision with a Chinese cargo ship yesterday morning. All six Hongkong crew members were safely rescued from the water by other fishing boats but Government officials are concerned that the mainland ship did not stop, offer assistance or report the incident. The 9,000-tonne Zijin Shan, identified by fishermen, is believed to have continued through Hongkong waters to Shekou. The Government will investigate whether the Chinese ship breached international maritime law by its failure to take action. Mr Wong Tai-hei, master of the Aberdeen-based fishing vessel, reported the loss of the boat when he returned to the harbour at 10 am yesterday. The owner of the boat, Mr Lai Kam-chuen, and his wife were also on board when it sank. ''A Chinese vessel collided with a Hongkong fishing vessel about 25 miles [40 km] east of Hongkong waters,'' a Government spokesman said. ''The six people on board, five men and one woman, were rescued by other fishing vessels nearby.'' The Marine Rescue Co-ordination Centre reported the incident to China's central Search and Rescue Centre in Beijing and to the Guangdong branch of the service. A Marine Department spokesman said: ''We are finding further information on the incident.'' But he admitted that as the collision happened outside Hongkong waters and involved a ship registered in another country, a full investigation was unlikely. On March 31, 11 Vietnamese seamen died and four were rescued after their 327-tonne cargo ship, Hai Long, sank after a collision with the 4,733-tonne Chinese ship , Hing Son, southwest of Lantau. On March 15, another Hongkong fishing vessel sank and four people, including a pregnant woman, died when their boat was in collision with a container ship in heavy fog, 12 kms south of Waglan Island.