About 28 percent of the people involved biker gangs are supported by the underworld, and 17 percent pay the mob for protection, according to a National Police Agency survey released Tuesday.

Many of the members are high school students, the survey says, noting that teens are forming yakuza links.

The survey, carried out every five years, was conducted from last June to July on 2,063 biker gang members and former members.

About 1 percent of the respondents said they belong to the underworld, while 14 percent said they had yakuza ties although they are not members. About 11 percent said they have been approached in the past to join the mob.