A 21-year-old homeless man has handed himself in to police over the sexual assault of a woman at a park in Melbourne's north at the weekend.

The woman managed to flee her attacker by stabbing him with his own knife after being sexually assaulted in Thornbury's Mayer Park on Saturday night.

Police and SES combed the park on Saturday night. Credit:Nine News

A man handed himself in at Preston police station about 11am on Monday and is being questioned by detectives.

The 32-year-old woman was walking a friend's dog through the park when she was approached by a man, who told her he had lost something, Detective Acting Inspector Janet Mitchell said on Sunday.