Two men charged with smuggling HK$6.1 million worth of suspected silver to the mainland will appear in court on Thursday morning.

The pair, aged 40 and 46, were arrested at the Heung Yuen Wai Boundary Control Point on Tuesday, as they tried to make their way to Shenzhen in a private car.

During Customs clearance, officers located three undeclared paper boxes in the boot. One of the men claimed the goods were milk formula and festive food items, and presented corresponding receipts.

But inspector Mok Ka-fai said X-ray scans revealed something else.

"During the inspection, we found that the three paper boxes were surprisingly heavy - each of them weighing over 70kg on average," he said.

"This raised our suspicions so we did an X-ray scan right away... Some images purported to show high-density items resembling metal, instead of food."

Officers seized about 219kg of silver concealed inside tin cans, mingled with other foodstuffs such as milk formula, cookies and egg rolls.

Senior investigator Li Tsz-wing said the duo could have evaded duty of about HK$800,000 had they successfully smuggled the dutiable goods across the border.

They were charged with one count of attempting to export unmanifested cargo, and were due to appear at Fanling Magistrates' Courts on Thursday.

Li believed soaring prices have incentivised criminals to smuggle precious metals out of Hong Kong for profit, adding more officers have been deployed at checkpoints as Lunar New Year approaches.