"Imprisonment is very much on the cards," Judge Robert Ronayne told Parkin.
The identities of the three complainants were suppressed under statutory law but their allegations were revealed last week in the District Court at Auckland as they testified against Parkin.
The first complainant alleged Parkin pushed his hand under her togs while at a Northland beach.
"When he stuck his finger inside of me … the pain and the jolt, it felt like something had broken inside me. It hurt terribly, it bloody hurt," she told the court.
On another occasion she alleged Parkin forced her to touch his groin.
The third complainant alleged that Parkin indecently assaulted her on a tramping trip while they were sharing a bunk bed.
Parkin's defence counsel Arthur Fairley disputed all of the charges but accepted Parkin's partial admission to the fourth charge, in which Parkin had admitted he had asked the second complainant if she wanted to touch his exposed erection.
But Parkin claimed nothing further happened.
Parkin was remanded on bail until May.
