The Japan Coast Guard has confiscated 300 kg of stimulant drugs worth about ¥20 billion from a Sierra Leone-registered ship anchored at the port of Moji in Kitakyushu, it was learned Wednesday.

The amount of drugs is the fourth-largest ever seized in Japan, according to the National Police Agency.

More than 10 boxes of drugs were discovered in a tank in the ship's engine room, investigative authorities said.

The coast guard arrested 12 Indonesian crew members of the ship and two other people waiting for the ship at the port on suspicion of violating the law against stimulant drugs.

The 859-ton freighter, the Universal, arrived at Moji on Monday, having traveled from a port in southern China. It was set to leave for Shanghai Tuesday, according to the local government.

Given the large amount of drugs, the coast guard and police suspect that yakuza or other criminal organizations may have been involved.