An asylum seeker advocate in Papua New Guinea says scores of the detainees have been injured, some seriously, as gangs of armed PNG police and locals attacked them in reprisals for a break out.

On Sunday, a meeting about the asylum seekers' resettlement claims ended in chaos with some of them rioting and breaking out of their compound.

An advocate, Ian Rintoul, says in response, all staff and guards were evacuated from the detention centre, leaving the asylum seekers defenceless against gangs and police.

He says the attacks started late on Monday night after the power to the facility was cut.

Locals armed with machetes, pipes, sticks and stones, attacked asylum seekers, with one reportedly thrown from the second floor of a building, and up to 50 in one compound suffering machete cuts.

Mr Rintoul says many asylum seekers have now fled, to avoid the attackers.

He says the Australian Immigration Department has blood on its hands and the Manus Island centre has always been a disaster waiting to happen.