About 90 refugees on Manus Island are sick and in dire need of medical care, Amnesty International says.

It's calling for food, water and medical treatment to be restored to the more-than 600 refugees and vulnerable men in the Lombrum detention centre before a major tragedy happens.

Amnesty International researcher Kate Schuetze has just returned from her third visit in four years to Manus Island.

She says she witnessed a desperate situation on the brink of catastrophe.

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Schuetze says she's just learned that about 90 men there are sick.

"We know that since Sunday last week they haven't been distributed with food or drinking water within the centre and on the 31st of October, power was cut."

Refugees told Schuetze they were concerned an attempt to remove them could result in violence.

"It's not safe for them to go outside, they have very real fears about their safety in the community because of the robberies and violent attacks that they told us about," she says.

"What these men need after four-and-a-half years on Manus Island, is to have their claims for protection met and right now, Australia is not doing that in Papua New Guinea."

Schuetze says it's going to be "a matter of days not weeks" before people start to get sick because of the lack of sanitation and clean drinking water.

She says there were three medical emergencies during her 10-day visit.

"In one case, a refugee who has epilepsy, had a fit and was unconscious for several hours. Refugees called guards to provide medical assistance but there was no response."

And a refugee with a known heart condition collapsed and nobody answered a call to an emergency number.

Amnesty International is calling on other countries to resettle the men, including for New Zealand to continue reiterating its offer to resettle some.

"There is no end in sight for these refugees until they're taken to a safe country where they can start to rebuild their lives," Schuetze says.