The women were sprayed with acid by a 41-year-old woman who has been detained by police, according to the Marseille prosecutor's office.
The news outlet reports two of the tourists were rushed to the hospital after having acid thrown in their face, while the other two suffer with burns.
Two of the US women suffered facial injuries in the attack, police said.
Four American women were attacked with acid in Marseille's main train station in France on Sunday, the city's prosecutor's office has just announced. All four women are in their early twenties.
Police do not believe the attack is terror related.
14 firefighters rushed to the scene in four emergency vehicles as the horror unfolded.
Reports say the acid was in a spray canister.