The National Police Agency said Thursday that 51 women were trafficked into Japan and forced to work in the adult entertainment industry in the first half of 2005, the highest figure on record for the first six months of a year.

Human rights groups and researchers, however, estimate that thousands of women, mostly from poor parts of Asia, are trafficked into Japan every year and forced to work in the sex industry.

The NPA figure is triple the number for the same period last year and includes a Thai transsexual -- the first time one has been recorded since the NPA began compiling the data in 2001.