A giant crane collapsed on a building site in Kwai Chung yesterday, hurling its operator to his death. Last night the cause of the accident remained a mystery. The 47-metre-high crane's horizontal arm was in motion at the time of the accident, but was not bearing any weight, police said. The operator, Wong Kwan-sing, 33, was in the control cabin atop the crane when it keeled over at the site in Wo Yi Hop Road, where developer Cheung Kong (Holdings) is building a hotel and serviced apartments. He was taken to Princess Margaret Hospital, where doctors declared him dead. A newspaper vendor whose stall is about 20 metres from the site heard a sound like thunder as the crane fell. 'Some metal parts flew out of the site. Pedestrians ran for shelter and I raced into a nearby restaurant,' he said. Police and firemen evacuated workers from the site and from a nearby car park. The crane's tower came to rest on the ground and its 30-metre arm against a partly built four-storey block. A section of scaffolding was badly damaged. Work on the site was suspended following the accident at 1.30pm while firemen and Labour Department officials investigated. A section of Wo Yi Hop Road was closed while the remains of the collapsed crane, one of three on the site, were demolished. Wong was not believed to have been wearing a safety belt, but a Labour Department spokeswoman said this was not a requirement of site safety regulations. The Hong Kong Construction Industry Employees' General Union called for the regulations to be toughened to avoid such an accident occurring again. Its chairman, Choi Chun-wa, while acknowledging accidents of this nature were rare, said: 'Contractors must make sure that cranes are properly installed and secured and regular maintenance should be carried out.' The accident is not the first involving cranes in the city. Two workmen died when a 60-metre crane collapsed at the Tsing Ma Bridge site on Tsing Yi Island in 1993. A man was killed in an accident the next year in Tsuen Wan.