A champion weightlifter - considered Australia's strongest man - has been accused of seducing and having sex with women as young as 17, while he was engaged to be married.

Daily Mail Australia reported three women have come forward with claims that professional weightlifter, 27-year old Rhyss Keane, sent them explicit messages and images and had sex with them behind his fiancee's back.

According to the report, Keane coached the women in his gym, affiliated with the Impact Christian church on New South Wales' central coast.

One 17-year-old girl told Australian TV show A Current Affair she met Keane at a powerlifting competition where he offered to be her coach - "a dream" for a young, enthusiastic lifter.

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"He would ask me to press against his groin region or allow him to do that to me," the girl said.

"It was fairly manipulative and controlling, I really felt like I had no option, that I had to do what he wanted for me to get the best coaching I could."

She also claims Keane sent her sexually explicit text messages including: "Will you show me your panties before you come so I can eye **** you and know what you're wearing?"

According to the girl, who admits to having sex with Keane on three occasions, the tattooed athlete "seemed infatuated" with getting her pregnant.

"I found that really strange. That's when I sort of stepped back a little bit and tried to evaluate what was really going on," she told A Current Affair.

Two other women interviewed have made similar claims. Details of Keane's alleged affairs reportedly emerged on the eve of his wedding to his now wife, Kayleigh.

The Daily Mail reported Keane issued an apology online after the claims emerged.

"I just wanted to take this time to sincerely apologise to you all, I have a serious problem and I have let people down I had a responsibility to you to be a leader and I failed, I am ashamed and embarrassed at myself," Keane posted on Facebook.

Keane is the Australian champion in his division and finished second in the 140 kilogram Pro Division at the World Powerlifting Championships in Moscow late last year.