One out of 5 high school students who use smartphones have communicated with strangers over the Internet and some have actually met them, according to a survey by the Tokyo Metropolitan Government, NHK reported.

The metropolitan government surveyed 1,500 elementary, junior high and high school students through their parents living in Tokyo last December on the use of mobile phones and smartphones, according to NHK. The poll found that 21 percent of the surveyed high school students had exchanged messages with strangers over the Internet, with a quarter of them responding that they have actually met people they got acquainted with over the Net, it said.

The figure was 6 percent for elementary school students and 15 percent for junior high school students, the report said.

The metropolitan government warns that students could get involved in crimes by communicating with strangers, calling on parents to talk with their children about the risks of using the Internet and urging them to create rules for using smartphones, NHK said.