Twelve people arrested early Thursday at Oi pier in Tokyo were among about 20 Chinese from Dalian suspected of entering Japan illegally, police said.
They arrested the six men and six women after receiving a report at around 12:45 a.m. that people were seen walking near Oi pier's No. 2 berth, which is closed to the public.
Several other Chinese fled the scene, according to police.
They said one of three cargo containers found at the scene looked as if people had been hiding in it. The containers were unloaded Wednesday from a ship that made a port of call at Kobe before coming to Tokyo, according to the people who were arrested.
The arrests came just hours after Kanagawa Prefectural Police detained 15 Chinese suspected of illegal entry at Honmoku pier in Yokohama, about 20 km south of Oi pier.
The eight women and seven men were held at the pier for failing to produce passports. Police had arrived at the scene after receiving a tip shortly after 6 p.m. Wednesday about some "suspicious people."
The detainees in Yokohama also told Kanagawa investigators that they came from China on a freighter and that about 20 people had hidden in a container.