The first happened on Friday night shortly before 00:00 GMT when a 40-year-old woman was approached by a man in a car pretending to be a taxi driver on Chatsworth Street in Pemberton.
She got into the blue vehicle, thinking it was a cab, and was raped.
The second attack happened at 22:00 GMT on Saturday in Mesnes Park, Wigan, when a 26-year-old woman was approached.
After a brief conservation with a man, she was threatened and raped.
The man in the second attack is described as in his 30s, 6ft tall and Asian. He was wearing a black tracksuit with a white stripe up the leg.
Sgt Adam Wall, of Greater Manchester Police, said: "We have had two reports of rape in 24 hours and had another suspicious incident reported to us this weekend in Wigan town centre which relates to a man who has approached a lone woman.
"I understand this will be worrying for people, especially at this time of year when people are out in the town centre for their Christmas parties."
He said patrols had been increased in Wigan town centre and surrounding areas.
Police are investigating two separate rapes of women in Wigan, Greater Manchester, during the weekend.