Several alleged smugglers are being held in connection with about 230 kg of stimulants seized at Yokohama port, investigative sources said.
The drugs have a street value of about ¥16.1 billion ($142 million), the sources said Wednesday.
The suspects include Mexican nationals. Some are likely to be served fresh arrest warrants on suspicion of breaking the stimulants control law, they said.
The drugs, discovered by Yokohama Customs in the middle of last year, were delivered in metal pipes imported from Mexico over several shipments dating back to around December 2015. Each pipe held about 5 kg of drugs.
The police broke the case using a technique called "controlled delivery," in which criminal activities are closely monitored until arrests are made.
The pipes were transported to a mountainous area in Sagamihara, Kanagawa Prefecture, after first being taken to Saitama Prefecture. In December, the police arrested some suspects who apparently visited the area to recover the drugs.
According to the Finance Ministry, the largest single seizure of illegal stimulants in Japan was about 597 kg, worth ¥42 billion, confiscated from a yacht moored at Naha port in Okinawa last May.