A young man was hit and killed by a speedboat while snorkelling off Sai Kung yesterday. Chan Lok-sun, 31, was snorkelling with a friend in Rocky Harbour, south of Sai Kung East Country Park, at around 12.45pm, police said. 'As the two were swimming back to their motor boat, the victim was hit by a speedboat,' a police spokesman said. Chan suffered serious head injuries and was left floating unconscious in the sea and his friend immediately signalled to his boat, asking for help. The injured man was brought on board the snorkellers' motor boat and ferried to shore before being picked up by a Government Flying Service helicopter. He was airlifted to Pamela Youde Nethersole Eastern Hospital in Chai Wan, where doctors declared him dead at 1.39pm. The speedboat was apparently being used for water skiing at the time of the incident. Last night the speedboat driver, a 21-year-old man, was arrested for endangering the safety of others at sea. Police said the speedboat had been taken to the headquarters of the Marine Police East division at Tui Min Hoi, Sai Kung, for a follow-up inspection. Its driver was helping police with their inquiries last night, and no arrests had been made. 'We are investigating why its driver failed to see the victim, and whether the speedboat was going too fast,' a senior police officer said. The Marine Department refused to comment on the case since it is still under police investigation. Three deaths were reported last year related to water-sports accidents, it said. A department spokeswoman said boat operators must keep a proper lookout of the waters around them.