A huge construction crane toppled onto a school building in western China, killing five people and injuring more than 90 students as it sliced through the structure, officials and state media said. "Four students aged under 12 and the operator of the crane were killed," said a city official of Tianshui city in the western province of Gansu. Nineteen students from the Tianshui school remained in hospital, including three in critical condition, he added. According to the Lanzhou Morning News, some 91 students were injured in the accident, which occurred Monday while children were attending their afternoon lessons. The crane was in use at a nearby construction site when it toppled over onto the school building and "tore through the three-storey building from roof to bottom," the newspaper said. The cause of the accident is still under investigation, but the official said a mechanical fault in the crane might be to blame. Dozens of frightened parents waited anxiously at two local hospitals while their children received treatment. "My son’s wounds are not severe but he obviously suffered severe mental trauma. He is scared of going to school," said Zhao Jinji, father of one 10-year-old victim. The accident offered another reminder of China’s poor safety standards. In July, the collapse of a gigantic gantry crane onto a Shanghai shipyard killed 36 people and prompted a broad investigation of the use of heavy machinery in the city.