Travellers to Tokyo are warned of a recent spate of gropings on trains that were inspired by websites.

Police have urged website operators to shut down them down and will deploy more officers on trains promoted on the sites as easy hunting grounds.

A 23 year-old was arrested in April on suspicion of indecently touching the lower body of a high school student on a train in Tokyo.  The man had travelled more than 100km from his home specifically target a train that was said to be easy pickings on a website.

When questioned by the police why he groped the girl, he said he had found a website that detailed how and when to grope people and wanted to confirm whether the hints worked.

Police say that between 1500 and 1800 arrests have been made each year for the past few years, with 708 arrests made in the first half of this year.

Police have expressed alarm at the number of suspects caught this year, including two men who were arrested in two separate incidents under suspicion of groping women on the Saikyo line, saying that they were inspired by the websites.

Over 100 websites allow people to exchange groping-related information for particular train lines, with some specifying which train cars and what times to target, police said.

The police department has planned to deploy more officers on the nine railway lines that are frequent targets by gropers.

The lines include JR Saikyo, Chuo, Sobu and Keio lines.