POLICE raided a heroin-cutting and distribution centre in Sai Kung yesterday, seizing 6kg of high-grade heroin and arresting two people. It was the latest in a series of operations following in-depth investigations by the specialist Narcotics Bureau, which is believed to have shut down four drug factories. Yesterday morning, officers staked out a village house in Kei Ling Ha Lo Wai on Sai Sha Road in Sai Kung. Shortly after 4am, they ambushed a man as he went from the house to a car, and found blocks of suspected heroin weighing about 1.4kg in the car. They then raided the second-floor flat, where they discovered a further 4.6kg of suspected heroin and equipment to dilute the drug. The man and a woman found in the flat, both 39, were arrested for trafficking in dangerous drugs. The narcotics seized in the operation were destined for local drug abusers and had a market value of $3.3 million, according to Senior Superintendent of the Narcotics Bureau Ng Kam-wing. 'The investigation is still going on, but we believe the man and the woman we have arrested are two key figures,' said Superintendent To Hon-ki. He said police were still looking for other members of the gang. In the past three weeks, a total of 19kg of heroin and 3kg of ice has been seized in five separate operations, including yesterday's raid. Five men and two women, aged between 22 and 39, have been arrested. The five gangs were not thought to be linked, Mr Ng said. The drugs seized during the five operations were worth an estimated $10 million on the street. The amount of drugs seized by the bureau in the first quarter of this year showed a 50 per cent increase on the same period last year, the officers said. Mr To said the rise did not mean Hong Kong had turned into an entrepot for drugs or that demand for narcotics was increasing. 'I would attribute the rise to improvements in the investigation method,' he said.