75 people are arrested during the operation against an illicit fuel business which police say was worth $140m a year At least 75 people have been arrested for involvement in a triad-run fuel business, operated on a huge scale in Tuen Mun. Police and customs officers who made the arrests over the weekend said the operation had annual profits of more than $140 million and was the largest operation of its kind in Hong Kong. They said that the operation's suspected mastermind was among those arrested. Operation Buttonhead was launched on Saturday night, targeting the Sun Yee On triad, which has its stronghold in Tuen Mun. The operation was continuing last night. The regional commander of New Territories North Police, Assistant Commissioner Steve Chandler, said the triad society had monopolised the manufacture and sale of illicit fuel in Tuen Mun for more than a year. The syndicate processed industrial oil and sold it as diesel. 'The storage and sales centre was raided more than six times last year and once in February this year. We believe the operation is the largest of its kind,' Dr Chandler said. More than 300 police and about 100 customs officers were involved in the operation. Officers seized 13 oil tankers and 16 other vehicles. They raided locations including an illicit oil treatment plant and storage facility in Nai Wai village, Tuen Mun, and 11 sales depots across Tsing Yi, Tsuen Wan, Sheung Shui and other places in the New Territories. Seven storage tanks in the Nai Wai plant, containing more than 20,000 litres of illicit fuel, were also found. Dr Chandler said the force believed the operation had devastated the Sun Yee On's main source of income. The business generated daily profits of about $400,000, according to Dr Chandler. Seventy-two men and three women, aged between 19 and 52, were arrested. A 46-year-old man was believed to be the mastermind of the syndicate. Three of those arrested were mainlanders with two-way permits, police said. By midnight last night, 43 of the suspects had been released on bail. Customs officers said that after previous raids, the illicit plant in Nai Wai had resumed operations almost immediately. Police are now considering going to the courts to confiscate the 30,000 sq ft site. Customs officers said the large amount of illicit oil at the facility posed a safety hazard to nearby residents. The Nai Wai plant was discovered in December 2002 after it caught fire. About 2,000 litres of illicit oil were found inside a hut on the site. Two weeks before the blaze, customs officers seized about 160,000 litres of illicit oil, worth almost $3 million, and arrested 30 men in a three-day operation at Lok Ma Chau and Man Kam To. Officers have previously warned motorists not to buy illicit fuel, which they said could be extremely dangerous.