A police report has been made against a debater accused of sexual harassment and behaving inappropriately towards the secondary school students he was coaching.

The Singaporean, who was not identified, allegedly sent sexually explicit photos of himself via WhatsApp to a student, who was a minor, said the Debate Association (Singapore) in a statement on Tuesday. He also allegedly had a "physical sexual encounter" with the student.

When contacted, the police said on Wednesday that they are "looking into the matter" after a report was made.

The Debate Association said that in 2014, the man allegedly sent the student sexually explicit photos of himself and pressured the student, who was part of a debate programme organised by the association, to send him similar photos.

The man, who was in his late 20s at the time, was director of the programme from 2012 to 2014. He is said to be a prominent and respected figure in debating circles.

He allegedly continued to pressure the student until the end of 2014, when he initiated and had a "physical sexual encounter" with the student, the statement said. By then, the student was no longer part of the programme.

The man also allegedly made sexual comments in a separate WhatsApp group chat with nine other students, where he discussed sex acts, sexual preferences and the sexual history of those in the group chat, the statement added.

He also "led discussions on the objectification of (students) who were minors" by sending photos of the students, and asking the group members to comment on their physical characteristics, including genitalia.

The association said it has since barred the man from future events, and informed partner organisations. He was notified of the ban on Tuesday.

"The executive committee has been in touch with all the students affected, and encouraged them to file their own police reports. It has also provided options for counselling and assistance from social organisations equipped to deal with such cases," the statement said.

In response to queries from The Straits Times, Debate Association (Singapore) president Cherylyn Wee said she had earlier heard about the allegations but could not act as none of those involved had come forward.

She said evidence came to light only recently after it reviewed the programme. She added that the association is "moving to create more robust and thorough processes in all our programmes to ensure such cases never happen again".