Papua New Guinea locals employed by security guards at the Manus Island detention centre attacked asylum seekers with machetes, knives and rocks, an interpreter employed by the Australian Immigration Department has claimed.

Azita Bokan alleges asylum seekers used plastic chairs as shields when they were attacked by locals who entered the centre on Monday night.

Immigration Minister Scott Morrison has increased the number of security guards at the centre by more than a third, following days of violence that left one asylum seeker dead and scores of others severely injured.

Ms Bokan says she saw people who had suffered ''massive head injuries'' when locals entered the centre after detainees had pushed down a fence within the centre.

''Definitely, 100 per cent, I stand by the statement that the local people, including some employed by [security contractor] G4S, they were the ones who caused this drama,'' Ms Bokan said after flying out of Manus Island on Wednesday.

Ms Bokan says she did not witness the violence, but was in the area where the injured were taken, and was told injuries were caused by machetes, knives, rocks and table legs. ''There was blood everywhere. The number injured was horrific: people with massive head injuries, at least one with a slashed throat,'' she said.

''The detainees, they grabbed these plastic chairs and were holding it in front of them to use it as a shield, not as a weapon.''

Mr Morrison said he had no ''verification or any clarification'' of the allegations. ''This is going to be a very difficult process … it was a very unruly incident,'' he said.

G4S issued a statement on Thursday morning saying it was concerned about allegations that its local staff may have been involved in the violence.

''Our duty of care to the transferees has always been and remains our highest priority. Our personnel on duty during the disturbances acted with courage, strength and determination to protect those in our care,'' the statement said.

The company also said its guards at Manus Island were not armed. It said it supported the investigation into the incident and would fully co-operate.

Ms Bokan said she had been employed by the department for 12 months and had been on Manus for a week. She claims unrest on Sunday was sparked when the detainees were pressured to voluntarily return to their homelands and told there was no prospect of resettlement in Australia, a third country or on Manus.

In explosive claims, Ms Bokan also says the asylum seekers had not complained about serious mental and other health concerns for months because they were told their claims would not be processed and that no other country would give them protection.

She said many asylum seekers suffered headaches, ear infections and such serious dental decay they had teeth pulled out by a local.

Ms Bokan said she intervened when guards attacked an asylum seeker the morning after Sunday night's unrest and implored authorities to ''let us talk and calm the situation down''. ''I said, 'Just give them some hope', but there was no hope to be given. We knew it was a bad night.''

She said she was ''disciplined'' by the Department when she intervened on behalf of an asylum seeker.

Documents show she was then suspended by the Department on Tuesday.

Ms Bokan said she was not allowed to speak to the media under the terms of her contract but could not remain silent.

''I am seeking a lawyer to protect me because I know they will come after me with all that they have.''

On Wednesday afternoon Mr Morrison announced he would be sending the commander of Operation Sovereign Borders, General Angus Campbell, and a team of security guards to Manus.

''After what has been a very difficult 48 hours, the centre is now operational,'' Mr Morrison said.

General Campbell will arrive in Manus on Thursday to assess the ''stability'' of the centre, Mr Morrison said.

Independent MP Clive Palmer has called for Mr Morrison's resignation, saying Mr Morrison had ''blood on his hands''.

Papua New Guinea Prime Minister Peter O'Neill has admitted that police fired gunshots but insisted they had not fired at asylum-seekers but rather for crowd-control purposes.

He rejected reports villagers had become involved in the violence.

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