Three men aged 33, 25 and 24 have been arrested on suspicion of rape in Wigan.
Two of the men stood by and watched as the third raped a woman in her 30s yesterday evening as she was out walking in Mesnes Park.
They all remain in custody for questioning.
Detective Sergeant Sarah Bell of GMP’s Wigan District said: “This was a despicable attack on a lone woman who is currently being supported by specialist officers.
“While we have arrested three people in connection with this incident, we are continuing to appeal to the public for information.
“Were you in the area at the time and do you have any information that can assist us? If so, contact police immediately.”