Twenty-one passengers were hurt last night after a collision between a packed China Motor Bus double-decker and a bus being towed near Aberdeen Tunnel. The No 590 bus carrying about 110 passengers was about to stop near the tunnel at Wong Chuk Hang when the tow truck driver changed lanes, sending the towed Citybus smashing into the rear of the CMB bus in front, police said. The accident happened at about 8.35 pm. Nine men and 12 women were taken to Queen Mary Hospital, where one passenger refused treatment. By midnight, 18 of the injured passengers had been discharged and three were still under observation. Ng Ying-chun, 11, had been sitting behind his mother on the rear seat on the bus' upper deck. 'There was a loud bang and I was thrown out of my seat. I don't know what happened,' he said. 'Windows were smashed and smoke was coming out from the engine. I was so scared that I grasped my mother.' He suffered cuts to his face and neck injuries.