A rock about the size of a hand struck a moving car with as much as 300lbs of force, smashing through the windscreen and killing the driver. Police said the rock – measuring 10cm by 15cm by 10cm and weighing 3 to 4kg – may have fallen from another vehicle. It went through a corner of the windscreen before hitting retired policeman Tam Chi-keung, 59, on the right side of his face. He was declared dead at the scene. READ MORE: Man, 70, killed by Hong Kong school bus in morning spate of road accidents The bizarre accident happened at about 6.50am yesterday on Cheung Sha Wan Road. Tam was driving to his Tsuen Wan home along the West Kowloon Corridor after taking his wife to Sai Ying Pun in Western district. After Tam was hit, his black Mazda MPV continued to drift for about 100 metres before it stopped beside a roadside barrier. Another driver called police. Chief Inspector Sun Lun-yum, from Traffic West Kowloon, said the police were looking at footage taken by a camera in the car. “From the driver’s perspective, it was unlikely he could avoid the rock, as it came towards him all of a sudden,” he said. Sun added that the rock appeared to be made of building material akin to a piece of granite. “It is not a brick or a natural rock.” A similar but smaller object was found nearby, he said. READ MORE: Malaysian tourist in Hong Kong killed in head-on motorcycle crash with car Registered engineer and mechanics expert Lo Kok-keung said: “Assuming the car and the rock were each travelling at the speed of 50km/h, the force of the shock would be up to 300 pounds.” He said vehicle windscreens in general could stand a shock of about 100lb to protect drivers from sand and tiny stones. “A shock of 300 pounds would definitely break the windscreen. It could smash the jaw bone,” the retired Polytechnic University engineer said. Lo believed the rock could have been tossed from another vehicle or been kicked up from the ground by the wheels of other vehicles. A shock of 300lbs would definitely break the windscreen. It could smash the jaw bone. Registered engineer and mechanics expert Lo Kok-keung Under the Road Traffic (Traffic Control) Regulations – Security of Loads, the driver of a motor vehicle on a road shall ensure that any load is properly secured to and contained on or inside the vehicle. A police spokeswoman said anyone in violation of the regulation would face a maximum penalty of a HK$10,000 fine and six-month’s jail. Police figures showed 821 people were prosecuted for failing to secure their loads properly on board their vehicles in the first 10 months of last year. A total of 891 people were prosecuted in the whole of 2014. The Highways Department is responsible for cleaning obstructions including rubbish on highways in the city. A spokeswoman said the department carried out regular patrols to check for any obstructions on highways and to clean or take action after receiving complaints.