A preliminary investigation suggested the smuggling operation was designed to evade import tariffs of about 10 per cent in Japan, he added.

“Smugglers could have evaded about HK$8.4 million in taxes if the precious metal was successfully smuggled into the country,” Lau said.

The consignment, bound for Tokyo and comprising two air compressors with a combined weight of 775kg (1,708lbs), was selected for inspection at the airport’s cargo terminal on March 27, according to the Customs and Excise Department.

Assistant Superintendent Ho Tin-hong of customs’ air cargo division said an X-ray examination revealed the two machines appeared suspicious.

“After removing the motor’s casing, we found its rotor was wrapped in a cord wheel which was tied with tape. It was not similar to a normal motor,” Ho said.

“We took out the rotor and found traces of glue on both ends. We tapped the rotor lightly with a hammer and noticed unevenness, suggesting the metal was somewhat fragile. Scraping off the paint revealed a gold-coloured surface.”

Further inspection led customs officers to discover another five gold parts in the shape of a motor rotor, a gear and three screw shafts, which were concealed in the machines’ motors and pumps.

“We believe the smugglers melted the gold under severe heat and put it into designated moulds to shape the precious metal into motor rotors, a gear and screw shafts, before painting it in silver colour to look like machine parts,” Lau said.

He said customs officers discovered a gold motor rotor and two other gold parts in each compressor.

The two rotors weighed 43.2kg and 45.3kg each, while the other four gold items had a total weight of 57.5kg, according to the department.

“We confiscated gold with a combined weight of 146kg concealed in the two machines,” Lau said. “The estimated value of the seized precious metal is HK$84 million.”

He said it was the biggest-ever seizure of smuggled gold in terms of value.

On Wednesday last week, customs officers arrested the director of a local company which was the consignor in the document.

Hong Kong customs arrests Macau chauffeur, seizes gold bars worth HK$10 million

“An initial investigation showed the firm had no actual business. We don’t rule out the possibility it was a shell company,” Lau said.

The 31-year-old man was detained on suspicion of attempting to export unmanifested cargo – an offence punishable by up to seven years in jail and a HK$2 million fine.

The acting senior superintendent said it was possible the gold parts in the shape of rotors and other machinery components were made in the city and then assembled in the machines.

Lau described the smuggling operation as “well-planned”, saying criminals turned gold into machine parts with “deep thinking and careful consideration”.

“They also made use of the strong structure of air compressors to conceal the heaviness of the gold in an attempt to avoid detection,” he said.

Lau said customs would exchange intelligence with overseas law enforcement agencies to determine the origin and the consignee of the precious metal.

“We have dealt a heavy blow against the cross-border gold smuggling syndicate because we confiscated HK$84 million worth of the precious metal,” he said.

The suspect was released on bail pending further investigation and more arrests were possible, customs said.

It was the third major gold-smuggling case customs officers discovered this year.

On February 22, officers arrested a Macau resident and seized gold bars worth HK$10 million hidden inside his car before he left Hong Kong via the world’s longest sea-crossing – the Hong Kong-Zhuhai-Macau Bridge.

Hong Kong customs arrests Macau resident after seizing HK$10 million in gold bars

It was the second such seizure in six weeks. On January 8, customs seized the same amount of gold bars hidden in a secret compartment under the centre console next to the driver’s seat of a vehicle. Its 32-year-old driver, also a Macau identity card holder, was arrested.

Customs officials believed the gold bars seized in the two cases were intended for mainland China, where smugglers could make a profit from the price difference.

Gold has been setting a series of records over the past couple of weeks and hit a fresh high of US$2,353.79 an ounce on Monday, driven by speculative buying and persistent tensions in the Middle East.