Customs officers have raided the largest and most sophisticated drug-making centre ever found in Hong Kong. The centre, in a Kwai Chung factory, was capable of producing 200kg of high-grade methamphetamine worth HK$150 million in three days. Customs officers seized finished and semi-finished batches of the drug Ice in liquid and crystal forms with a street value of HK$175 million and four sets of drug-making machines from the factory and two other locations. Among the seizures was 67.5kg of Ice, the first batch the syndicate had produced, which was found in a hotel room in the New Territories used as a storage centre. Investigators are puzzled why the centre was set up in Hong Kong as such operations are usually based on the mainland. A mainland expert on drug production and a Hong Kong family of four were arrested in the operation after 30 officers carried out round-the-clock surveillance for four days. 'It's the first time such a sophisticated drug-making centre has been discovered in Hong Kong. It's also the largest drug-producing centre we have busted,' said Senior Superintendent John Lee Cheung-wing, head of Customs' Drug Investigation Bureau. He said it was also a record seizure of Ice in Hong Kong. Some 44kg of the drug was seized last year, and 24kg in 2008. Lee believes the centre had been operating for one or two months. He said preliminary investigations showed the drugs were intended for Southeast Asian countries, although a small amount may have been for local consumption. Lee said there was no evidence that Hong Kong was being used as a drug-manufacturing centre. 'It's an isolated case.' The 3,000 sq ft centre on the top floor of an industrial building in Kwai Chung was equipped with closed-circuit TV and had a pinhole camera concealed in the main gate to monitor the area outside the factory, said Superintendent Wong Pak-tong. 'During the 100-hour round-the-clock surveillance, our officers had to hide in rear staircases or the roof of the building to monitor the centre,' he said. 'Officers were also disguised as delivery workers and decoration workers during the surveillance.' Wong said the four rotary evaporators used to make the drug were connected to a filtering machine that absorbed the chemical smell emitted during drug-making All the windows of the factory were closed and boarded up. Officers said chemicals used to make the drug could release toxic gas and cause an explosion. Last night officers were still investigating how the syndicate obtained the controlled chemical - Phenyl-2-propanone - to make the drugs. Lee said it was possible the chemical was smuggled into Hong Kong. Customs began investigating the syndicate after exchanging intelligence with mainland authorities about a month ago. After finding the centre and identifying key figures of the syndicate, officers raided the centre and arrested the 45-year-old mainland man and the alleged ringleader, aged 55, on Wednesday night. The mainlander had arrived in Hong Kong on Friday last week. He went straight to the drug factory and had not left since. Inside the centre, customs officers seized 270 litres of the drug solution in finished and semi-finished form and the four rotary evaporators that could turn the solution into 160kg of illegal drugs. There were several hundreds of kilograms of other chemicals that were used as drug additives. During the raid on the hotel room officers seized three suitcases containing 67.5kg of Ice and arrested the 25-year-old son of the alleged ringleader. At the same time, another team of officers arrested the 60-year-old wife and 28-year-old son of the alleged ringleader and seized 2.5kg of the drug in the family's flat in Jordan. The five suspects were still being questioned yesterday. Wong said they were likely to be charged with manufacturing and trafficking dangerous drugs.