Police have seized more than HK$50 million worth of crack cocaine, and the raw material used in its preparation, in the biggest home-manufactured drugs bust in 10 years.
The raid, on a 1,000-square-foot Yuen Long apartment on Friday, also yielded flammable chemicals and tools.
Police said a man, thought to be of Peruvian origin, was believed to have been flown in to extract cocaine from a powdered mixture smuggled into Hong Kong in air cargo.
He was arrested along with three local males on suspicion of manufacturing drugs.
Officers said they believe none of the cocaine made had actually reached the market.
Chief Superintendent Ma Ping-yiu said it was the first time the force had come across a syndicate renting an upmarket flat for the purpose of making drugs.
"One of the reasons is to try to make it less suspicious for law enforcement and make it more difficult for us to detect the case," Ma said.
Police also said the flat was rented last month and the gang could have taken the raw materials in in boxes while pretending to move in. Officers added that the gang might have thought that a bigger flat would help dilute the strong smells generated in the drug-making process.
The force said the raid was conducted following an investigation that lasted for months and more arrests could follow.