A man has been charged with sexually assaulting a teenage male who had passed out at a Sydney railway platform.

After a night out with friends, a heavily intoxicated 18-year-old went to sleep on a platform at Central railway station in the early hours of January 18, police say.

He allegedly awoke sometime later to find another man performing a lewd act on him.

The young male rang police while the other man fled the scene.

Following further inquiries, police arrested a 58-year-old man at a hotel in Darling Harbour on Thursday.

He was charged with sexual intercourse without consent and was refused bail to appear in Central Local Court on Friday.

The Sex Crimes Squad had formed Strike Force Merinda to investigate sexual assaults of a similar nature between 2009 and 2013.

Anyone who has not already reported such a matter is urged to contact Crime Stoppers on 1800 333 000.