In the report This Is Still Breaking People, Amnesty claims the living conditions on Manus Island breach international standards, with asylum seekers living in cramped and dirty conditions and expected to sleep on thin mattresses on the floor. In the most populated compound, 414 asylum seekers live in close quarters, the report says.

The report also reveals the use of a small, makeshift, separate compound where mentally ill patients are guarded, there is no air flow and asylum seekers must be escorted to the toilet. The mental health team leader for health services provider International Health and Medical Services (IHMS), Gareth Lee, says in the report there was no full-time psychiatrist at the centre.

A spokesman for Immigration Minister Scott Morrison said the mentally ill asylum seekers referred to in the report were accommodated in single rooms.

The report comes as the government has passed amendments to the Migration Act that will leave asylum seekers in indefinite detention if they receive an adverse security assessment by ASIO.

Kate Schuetze, Amnesty's Pacific researcher and one of the report's authors, said she was shocked to see the visible trauma of the people being held in the makeshift psychiatric ward when she visited the centre in March.

''There was one person visibly shaking and trembling and saying he had been like that since the violence,'' she said. ''Also reports about the deterioration of mental health and people being on hunger strikes for more than 20 days.''

Ms Schuetze said tension was palpable at the centre following the violence in February that killed one asylum seeker. ''Without any real attempts to address the uncertainty and indefinite detention of asylum seekers, the situation will remain volatile, and further violence is inevitable,'' the report says.

But gaining access to Australia's offshore detention centre has become increasingly difficult. Both Amnesty International and the United Nations Special Rapporteur have been denied access to Nauru since March. The Special Rapporteur was also refused a meeting with security firm G4S. Most witness accounts from the violence say local G4S guards were responsible for most of it.

The report concludes that offshore processing should end immediately to guarantee the right to life and security. It also recommends that mentally ill patients be removed from confined living areas and be given immediate access to full-time psychiatric care.

Meanwhile, changes to the Migration Act that were passed in the Senate on Wednesday by Labor and the Coalition have been heavily criticised by human rights advocates and the Greens, who say they are ''cruel and unnecessary''.

''This bill will see dozens of refugees who have received secretive adverse ASIO assessments locked up on Australian soil, without charge and with no chance of release,'' Greens immigration spokeswoman Sarah Hanson-Young said.

In February the intelligence watchdog criticised ASIO for ''inconsistent and arbitrary'' practices by denying some refugees legal representation.

In changes to the act, the minister's decisions on visas will be effective immediately and if a person is denied a permanent protection visa they can never apply for one again.

Mr Morrison's spokesman said the Immigration Department was trying to recruit a full-time psychiatrist to work on Manus Island.

“The Minister was wrongly advised by his department on this matter," the spokesman said. "The Minister is advised that in January this year IHMS identified the need for a full time psychiatrist service at the Manus Offshore Processing Centre.  The department supported the proposal and requested IHMS commence recruitment of suitable staff to provide these services.

“The full time psychiatrist role was filled in February by rotations. At any time, a full time service may be disrupted by short term vacancies, illness or other events.

“The planned deployments were disrupted by the events of February 2014.  The Minister is advised IHMS is undertaking recruitment now to have the full time coverage back in place.”

The spokesman also said the population at Manus Island was falling. There was spare capacity at the centre and further infrastructure was being built.