Police have found that disco patrons are buying Ecstasy and ketamine wheeled out on trolleys, in the same way that dim sum is sold in restaurants. The discovery was made weeks ago when two female officers began an undercover operation at three Mongkok discos run by the 14K triad gang - surveillance that ended yesterday with a huge raid resulting in 16 arrests and a seizure of $55,000 worth of Ecstasy, ketamine, Erimin 5, cannabis and cocaine. At several points in the evening, disco staff would push out the trolleys, and the clients, familiar with the drill, would line up to make their purchases. Following the raids at the discos yesterday the police operations officer for the Mongkok district, Tony Siu Kit-hung, said it was the first time they had seen the dim sum-style selling. It took almost two weeks for the officers to win entry to the discos. Bouncers would turn away a new face unless they were accompanied by known clients. The criminals had even put lookouts outside the Mongkok police station to spot signs of impending operations, and would send a warning back to the discos if there was any indication of a police raid. Aware that the lookouts had been stationed, police officers yesterday had first scattered across Mongkok before raiding the three discos, located in one building in Mongkok Road. More than 70 officers took part in the raid. Ten men and six women, aged between 19 and 57, were arrested after police searched about 400 people in the discos. They were released on bail last night as investigations into the drugs den continued. It is believed that some of the gangsters managed to get rid of some drugs before the police arrived as the drugs trolley could not be located in the raid. Apart from drugs, the police also seized a small quantity of weapons such as extendable batons at the discos.