Almost all of the people who have accessed a Justice Ministry Web site where they can report "suspicious" foreigners have done so anonymously, Amnesty International Japan said Friday.

The system, introduced Feb. 16, has drawn harsh criticism from human rights groups for promoting racism and violating foreigners' privacy.

"The rampant anonymousness will further urge people to be involved in the discriminative reporting system," said Makoto Teranaka, secretary general at Amnesty International Japan.

Responding to their request to show detailed data about the informants, the ministry said it had received about 4,900 reports by the end of October, of which nearly 90 percent were anonymous, according to Amnesty.

Based on the reports, the ministry detected some 200 foreigners who were staying illegally in Japan, according to Amnesty.

In a separate development, the ministry said Friday that about 4,150 foreigners turned themselves in at immigration offices during the last two months of 2004 for overstaying their visas.

The figure for the period from Nov. 1 to Dec. 31 marks an increase of more than 40 percent from the same period the previous year, ministry officials said.

The tally came amid regulatory changes on Dec. 2 that allow overstayers to turn themselves in and immediately leave the country without detention in exchange for lighter punishment -- a one-year ban on re-entry instead of a five-year ban.