Four people have been arrested on suspicion of possessing about 100 kilograms of stimulant drugs on a ferry in Kagoshima Prefecture, police said.

The drugs, with a street value of some ¥7 billion ($62 million), are likely to have been smuggled into Japan via an islet off the main island of Kyushu, according to the police.

The suspects, including Hirotaka Tanaka, a 49-year-old senior member of a group linked to the Kobe Yamaguchi-gumi crime syndicate, are alleged to have had the drugs in a car aboard the ferry at a port in the city of Kagoshima on Wednesday.

The police said the drugs, found inside 10 separate sandbags, were meant for sale.

The contraband is said to have been handed over to the suspects while at sea from another vessel, believed to have come from overseas.

The drugs were then unloaded on Tokunoshima Island in Kagoshima earlier this month before being shipped to the city of Kagoshima in a car aboard the ferry, the police said.

The police are investigating whether stimulant drugs like those seized in Kagoshima were a source of income for the Kobe Yamaguchi-gumi yakuza group.