Suspected smugglers were caught trying to hide $10 million of gold by painting it silver and disguising it as machinery on a cargo plane

• Hong Kong customs officials discovered 146 kilograms of suspected gold on board a freight plane headed for Japan. 
• They say it is the largest gold-smuggling case on record in terms of value.
• A 31-year-old man was arrested in connection with the case. 

Hong Kong customs officials have seized 146 kilograms of suspected gold, worth more than $10 million, on board a freight plane headed for Japan.

The discovery is the largest gold-smuggling case on record in Hong Kong in terms of seizure value, according to the Customs Department.

The precious metal was discovered on 27 March while officials at Hong Kong International Airport examined two air compressors scheduled to be shipped by air freight to Japan.

Air compressors have various industrial and mining uses and are commonly used to fill gas cylinders used in diving. They are typically made of cast iron or aluminum.

But during an x-ray of the air compressors, officials discovered that gold had been carefully molded and "concealed in the integral parts" of the machinery.

The gold parts had been painted silver to match the machine parts, officials told local news outlet, the South China Morning Post (SCMP).

Acting Senior Superintendent Jason Lau Yuk-lung said it was the first time the department had discovered smugglers using this method of hiding gold, according to SCMP.

The gold was likely hidden to avoid Japan's import tariffs of around 10%, he said.

"Smugglers could have evaded about HK$8.4 million ($1 million) in taxes if the precious metal was successfully smuggled into the country," Lau told the outlet.

A 31-year-old man was arrested on April 3 in Hong Kong in connection with the case, officials said in a statement. He has been released on bail pending further investigation.

The man was the director of a local company, but Lau said there was a possibility it was a shell company.

Anyone found guilty of importing or exporting unmanifested cargo could be fined up to $2 million and imprisoned for up to seven years under Hong Kong laws.