NSW Police have successfully charged and extradited an alleged child sex-offender after he fled to the other side of the country.

The 32-year-old man was on a train at Central Station bound for Parramatta, shortly after the New Year’s Day fireworks.

A 12-year-old girl and her family were sitting next to the man when he reportedly incidentally assaulted the girl.

Police allege the man typed his phone number on his phone and showed it to the girl before getting off the train at Granville Station.

When the girl told her family what happened, they reported the incident to police.

Detective Chief Inspector Brad Monk tells Ben Fordham his team was determined to track down the alleged offender.

“We were determined to track this person down.

“We launched a media campaign and luckily we received information that identified who that person was.”

He tells Ben investigators were able to locate the man in Perth, on the other side of the country.

“We successfully extradited him back to NSW over the weekend.”

Detective Chief Inspector Monk says when the offender caught whiff they were on his tail, he fled to Canberra from where he caught a flight to Perth.

The man will front Parramatta Local Court on Wednesday.

Listen to the full interview below