Around 3.30am on Saturday, a woman in her 30s was walking along Lonsdale Road in Heaton when she was approached by a man.
He dragged her into a side street on Back Mornington Road and attempted to remove her clothing, tearing them in the process.
The woman managed to fight off the offender and ran to a place of safety.
The offender had his face covered and he was wearing a hooded jacket.
Detective Sergeant Andy Darnton, from GMP’s Bolton CID, said: “This was a terrifying ordeal for this woman, and she is currently being supported by specially trained officers.
“No one should be subjected to this kind of attack, and we are doing everything in our power to find the man responsible.
“If you saw anyone acting suspiciously in the area, or if you have any information which could help this investigation, then please get in touch with us as soon as you can.
Anyone with information should call police on 0161 856 5757 or 101 quoting incident number 466 of 05/01/2019, or the independent charity Crimestoppers, anonymously, on 0800 555 111.