A sex predator is believed to be behind five attacks on women in the CBD over the past three months.


In the most recent assault, a 22-year-old was attacked in a building stairwell after a man dragged her away from walking to Southern Cross Station.


The victim was walking on Flinders Lane when the man approached her from behind.


He grabbed her neck, told her to be quiet, and forced her to walk west along Flinders Lane, right into Spencer Street and then left into Collins Street.


They walked past Southern Cross Station and into a stairwell at 700 Collins Street, where he sexually assaulted her.


It is believed the man also stalked three young females at Southern Cross station earlier that morning about 5am.


The man followed each of the victims into the female toilets but the women locked themselves in toilet cubicles and called police before the man fled from the station.


After reviewing footage of the incidents taken from closed circuit television, detectives believe the man may also be responsible for two other serious sexual assaults in South Melbourne and the CBD in November and December last year.


In the early hours of December 7, a 24-year-old woman was assaulted at a Kings Way car dealership.


On November 9, a 22-year-old woman was assaulted along Bourke Street between Queen and King streets between 12.30am and 1.15am.


The man is described as Asian or South American in appearance, aged in his late teens to mid 20s, and with a slim build. He is believed to be about 165 centimetres tall.


Police also want to speak to another man who is shown talking to the offender on CCTV on November 9 outside a licensed premises at Melbourne Central.


Anyone with information is asked to phone Crime Stoppers on 1800 333 000.