Customs authorities seized 6,236 kilograms of gold smuggled into Japan in 2017, a new one-year high, government data showed Friday.

Based on the average price of around ¥4,500 per gram last year, the seized gold was worth around ¥28 billion ($261 million). Smugglers try to evade the 8 percent consumption tax levied on imports of gold worth over ¥200,000 and resell it at a tax-inclusive price.

Gold smuggling has been on the rise since Japan raised the consumption tax from 5 percent in 2014.

The number of gold smuggling cases handled by the authorities jumped 66 percent to 1,347 from 811 in 2016, the Finance Ministry said in its report.

Ninety-four percent of the cases involved air travelers, who collectively tried to smuggle 4,779 kg of gold into Japan. Most of the smuggled gold came from South Korea, Hong Kong and Taiwan.

Alarmed by the recent surge, Japan has been stepping up customs inspections and is planning to impose stricter penalties on perpetrators.

The possession of gold is not illegal, which authorities believe helps lower the psychological barrier for smuggling.

According to Finance Ministry data, the number of smuggling cases stood at 12 in 2013 but surged to 119 in 2014.

As for illegal stimulants, customs authorities seized 1,159 kg with a street value of around ¥74.2 billion in 2017, down 23 percent from a year earlier.

The amount of smuggled stimulants from Thailand and Malaysia rose, however, with young women in their 20s and 30s traveling by air involved in many cases, according to the ministry.