Eleven people were found in a shipping container offloaded at Tokyo port Thursday and were taken into custody on suspicion of entering the country illegally, police said.
The nine men and two women, who said they were aged between 19 and 34, were arrested for entering the country without a passport. Most are believed to be from China's Fujian Province.
The Metropolitan Police Department is investigating the incident as a case of mass human smuggling.
The 9,400-ton Panamanian-registered freighter that carried the container arrived at Oi Pier in Shinagawa Ward at around 6:30 p.m. Wednesday.
The SITC Shanghai left Dalian on Sunday before arriving in Tokyo via Nagoya. It left for Yokohama on Thursday morning after offloading some of its freight.
An employee of a berth-management company alerted customs officials after finding that the tag attached to the container did not match the one on his receipt, police said.
The people were found when customs agents and police opened the container.