Pretending to have supernatural powers, a bogus teenage medium duped two underage girls into having sex with him.

Alva Quek Sui Hong, now 20, had told the two friends they were being followed by malevolent spirits that would harm them and their loved ones if they did not have sex with him. The girls complied out of fear.

Quek, who is jobless, also sexually assaulted a third underage girl after he responded to her online advertisement for a gym partner, the court heard.

He was jailed for five years and nine months yesterday, after he pleaded guilty last month to five counts of sexually penetrating the three minors. He also admitted to one count of harassing a 22-year-old man.

One of the victims, a 14-year-old girl, first met Quek at Redhill MRT station on Dec 9, 2016.

He was with her group of friends that included the second victim, who was then 15 years old.

He later told the younger girl she was "followed by spirits" and he could ward them off. The group then went to Sentosa's Tanjong Beach for her to undergo a "cleansing ritual".

During the so-called ritual, Quek pretended to be possessed by a ghost and changed his voice when he spoke to her.

He then claimed he, the girl and the second victim would die if she did not have sex with him. He also told the 14-year-old to break up with her boyfriend.

The frightened girl did as she was told and Quek had sexual intercourse with her in a toilet behind Tanjong Beach Club on Dec 10, 2016.

Four days later, he similarly duped the 15-year-old into having sex with him in a Geylang hotel room. The older girl told the police about her ordeal the next day and officers arrested Quek on Dec 16, 2016.

He was out on bail when he responded in September last year to the online advertisement of the third minor, also aged 15.

They met in Hougang the following month and went to a multi-storey carpark at Block 475 Upper Serangoon Crescent.

While chatting, Quek kissed the girl's cheek before sexually assaulting her.

Deputy Public Prosecutor Nicholas Lai said that, throughout the ordeal, the girl was shocked by what was being done to her, and did not know what to do. "This was, after all, the very first time she met the accused in person. She tried to push the accused's hand away but the accused said 'don't stop me'."

She made a police report on Oct 25 last year, the court heard.

Quek also harassed a 22-year-old man in February last year by phoning him repeatedly to ask for monthly loans of $500.

Pretending again to have supernatural powers, he said misfortune would befall the man if he did not comply.

The man made a police report on March 21 last year.