Photo/Illutration A house where a massive trove of fake ID cards and counterfeiting materials was discovered in Asahi, Chiba Prefecture, on Sept. 28 (Yuji Masuyama)

Police have arrested six Japanese and Chinese nationals in connection with the alleged sale of counterfeit residence cards through foreign brokers.

A joint investigation team, comprising members of the Tokyo Metropolitan Police Department and five prefectural police departments, announced on Sept. 29 it busted six people, aged 29 to 34, on suspicion of violating the Immigration Control Law.

Investigators seized more than 200 fake IDs, including residence cards, from a house in Asahi, Chiba Prefecture.

Police said it is the largest base for card counterfeiting they have ever uncovered in Japan.

According to the announcement, the six are suspected of conspiring to provide two counterfeit residence cards to a Vietnamese broker in Ibaraki Prefecture in January.

Three of the six were arrested on suspicion of making 42 falsified residence cards with a computer and printer set up at the house around Sept. 5.

Many of these cards were sold to people from other countries through brokers and used as identification cards when the holder gets a job or purchases a cellphone, according to police.

A computer seized from the house contained a list of around 20,000 people, including Vietnamese, Indonesian and French nationals.

In addition to the fake residence cards, counterfeit driver’s licenses, health insurance cards and individual number cards were found at the house. So were approximately 3,000 blank plastic cards that had not yet been printed on and about 500 hologram stickers to be attached to the surface of the cards.

Police said they believe the counterfeit operation was under the direction of another person from China. Police believe that under this person’s orders, the six sold counterfeit residence cards to Vietnamese and Chinese nationals at prices ranging from 1,500 yen ($10) to 7,000 yen a piece through brokers.

Police believe the group made some 140 million yen since August last year by selling the fake cards.