Ian Rintoul of the Refugee Action Coalition says more than 50 detainees were seriously hurt when locals stormed the camp.
Australia's immigration minister, Scott Morrison, has confirmed a serious incident at the centre overnight.
He says he has been advised that PNG police did not enter the centre and only dealt with people who tried to escape.
But Ian Rintoul says the asylum seekers escaped to flee the attack.
"People fled for their lives when the locals and the police attacked last night, it's quite possible that perimeter fences have been breached in that process but I think it's incorrect to call it a break-out. People were fleeing for their lives when the PNG police and locals attacked the compounds."