A 32-year-old woman is fighting for her life after being hit by a car in Melbourne's north.

A passer-by found the woman on Clarendon Street in Thornbury about 2.50am on Sunday.

The woman, from Thornbury, was taken to the Royal Melbourne Hospital in a critical condition.

An 18-year-old Reservoir man presented himself and his vehicle to Northcote Police Station at 4.30am.

A Victoria Police spokeswoman said the teenager was later released without charge, but investigations were ongoing.

Police are asking anyone who may have seen a late-model Burgundy BMW sedan in the area at that time, or anyone with information on the incident, to contact Crime Stoppers on 1800 333 000 or to visit www.crimestoppers.com.au.