The second attack took place on the afternoon of May 1, when a 20-year-old woman was walking in Campbell St near Plymouth St. A man grabbed her from behind and forced her into a nearby property. She fought off her attacker, who ran off along Campbell St toward Plymouth St.
The woman was uninjured.
She described her attacker as Maori, 17 to 23 years old with thick eyebrows, large lips, and "blank eyes", wearing grey trackpants, a black T-shirt with a logo on the front, carrying a black backpack with zips and small writing in grey or white.
Whanganui Police Senior Sergeant Lance Kennedy said they could not confirm the two attacks were related, but it was concerning that they were similar in nature and timing.
The attacks appeared sexually motivated and had potential to end a lot worse for the victims, he said.
Mr Kennedy encouraged woman not to head out alone until an the offender or offenders were located.
Anyone with information relating to the attacks should contact Whanganui Police on 06 3490600, or provide information anonymously through Crimestoppers 0800 555 111.