A convicted child rapist has been arrested for assaulting two young teenage girls just hours after he was granted parole on Monday.

The 26-year-old man was on his way home from jail on a train where he met one of his victims, Seven News reported.

The man took the girl to Best Road Reserve in Seven Hills at about 3.30pm.

He then allegedly indecently and sexually assaulted the teenager and one of her friends, police said.

The girls, aged 15 and 16-years-old, left the park and were taken to Blacktown Hospital, where the alleged assaults were reported to police.