The piercing pain in Joinul Islam’s right arm keeps him from sleeping. He can’t bend it to eat properly (to eat with one’s left is considered unclean), and there are precious few painkillers to allow him to rest.

Four months ago, he was attacked by a gang in Lorengau, his elbow was sliced open with a machete and the surgery to repair it did not work. He was promised follow-up surgery, but it never happened. Now, he waits for more medical treatment that might never come.

In the meantime, he bears the pain – his right arm fused at an awkward angle – without assistance. He has been told by Papaua New Guinea authorities he can get more painkillers, but only in Lorengau, the place where he was attacked.

“I cannot go back there, I cannot go back. How can I go to Lorengau? I need a safe place,” he says.

Seated in a quiet corner of the darkened Manus Island detention centre, he speaks barely above a whisper. The pain, at one point, kept him awake for two weeks, he says. “I am so tired,” he tells the Guardian, as tears well in his eyes.

Islam has been formally recognised as a refugee, having fled persecution in his homeland Bangladesh. “My country, political is problem, is not safe. For safe place, I come to Australia.”

Islam says he feels under intense pressure to quit the Manus Island detention centre, even to abandon his claim for protection altogether, and risk returning to Bangladesh. “All the time is pressure. My life is very difficult. I have been running five years. Too long,” he says.

Islam’s case is barely remarkable inside the condemned the Manus Island detention centre – officially shuttered on 31 October, with all essential services withdrawn.

Hygiene conditions are worsening day by day. We are thirsty and have been waiting for rain Behrouz Boochani

There are few uninjured or healthy people among the 400 who remain in the camp, surviving on rainwater and makeshift wells, smuggled food, and solar panels powering phones that give them a link to the outside world.

Inside the camp, the Guardian saw men who, while walking through the wreckage of the site, had stepped on nails that had pierced their feet. Their infected wounds wept pus as they walked. Others revealed open and infected sores on their legs – cognisant that Iranian asylum seeker Hamid Kehazaei died after a small infection that, even with medical intervention, spiralled rapidly out of control in the detention centre and ultimately killed him.

Refugees at the condemned Manus Island detention centre. Authorities have destroyed shelters and makeshift water-collecting bins. Photograph: AFP/Getty Images

Nearly three weeks after the camp was formally closed, the medical situation in the condemned Manus Island detention centre has reached a new, even more dangerous stage. Even men who appear healthy are battling diarrhoea and vomiting brought on by drinking salty, contaminated water pulled from makeshift wells.

On Saturday Australian Medical Association members voted unanimously to call on the Australian government to grant access for doctors to be allowed into the detention centre to intervene in what the association describes as “a worsening and dangerous situation emerging on Manus”.

“It is our responsibility as a nation with a strong human rights record to ensure that we look after the health and wellbeing of these men, and provide them with safe and hygienic living conditions,” the AMA president, Michael Gannon, said.

Periodically, Papua New Guinean police and immigration officials – on Australian orders, the Guardian was told – enter and poison the wells, befouling them with dirt and rubbish and making the water undrinkable.

The men have some purification tablets and boil what they can, but their situation is unsustainable. “We have a new hard problem these days,” Iranian refugee Behrouz Boochani says. “The toilets are full and there’s a bad smell spreading in the prison camp. Hygiene conditions are worsening day by day. Hope we have some rain today to wash away the bad smell.

“The situation in Manus is critical. We are thirsty and have been waiting for rain in the past few days. We have some water we’re rationing but it’s not enough in tropical heat. Immigration destroyed the water we’d collected from tropical rain.”

A refugee pulls water from a makeshift well inside the Manus Island detention centre. Photograph: Ben Doherty/The Guardian

David Yapu, the police commander on Manus, has said fear of a widespread outbreak of potentially fatal illness was very real. “The centre is unhygienic, it is subject to illness such as typhoid, cholera and dysentery,” he says.

Cholera, most often spread by unsafe water, is easily treatable with the correct medication, but without it, the infection can kill in hours.

There is a meagre and dwindling cache of medical supplies inside the camp – and a fraught supply chain bringing more in – but refugees fear what will happen when these run out. Several refugees have become the unofficial medical officers of the camp, dispensing what medications they have.

“Even when IHMS [International Health and Medical Services] were here,” one refugee says, “this all we got. Panadol and water. Whatever was wrong with you: panadol and water.”

Refugees boil water in the detention centre

Many of the men, after four years in indefinite detention, have been on antidepressant medication or reliant on an ever-increasing regimen of sleeping pills. These are almost extinguished now.

The Australian immigration minister, Peter Dutton, said in a television interview last week the refugees still inside the Manus Island detention centre should leave it immediately, spruiking the alternative healthcare available.

“People are squatting illegally on this maritime base and we want them to move peacefully. There are buses available; people can move to a new $10m facility where they have accommodation, they’ve got kitchens, they have running water, all of the services that you could imagine, including health services, security, etc; but people are trying to make a political statement by staying at the regional processing centre.”

While there is greater access to healthcare for the refugees and asylum seekers who have moved to the alternative accommodation elsewhere in Lorengau province, this remains limited. The proposed accommodation centres are still being built, with limited running water and unreliable electricity. Refugees confirmed on Monday there is still no running water in the new West Lorengau centre. Seriously ill refugees are moved to Lorengau hospital, but that is in a state of disrepair and decay. The hospital is already far beyond its capacity, it has few working diagnostic machines, and regularly runs out of medicine itself.

Alternative accommodation in Lorengau is still being built, despite assurances from the Australian government that the camp is habitable. Photograph: Refugee Action Coalition/EPA

When a refugee was transported to Lorengau hospital from the detention centre two weeks ago suffering from what was believed to be a heart attack, the hospital’s only ECG machine was broken.

Nurses were able only to take the man’s blood pressure before discharging him and sending him to alternative accommodation in Lorengau. The Guardian met the man in Lorengau; he has not had any follow-up treatment.

Those refugees and asylum seekers who are sicker still are sent to Pacific International hospital in Port Moresby for treatment, but even here, there is often little treatment offered.

There are more than 120 refugees and asylum seekers housed – at Australian expense – in hotels around Port Moresby. One hotel has been booked in its entirety for several months with refugees and asylum seekers from Manus. Australian Border Force officials are housed nearby.

In the capital, the Guardian met more than a dozen refugees and asylum seekers awaiting treatment.

Some have been in Moresby two months and have had a single appointment, with no follow-up scheduled. There are also several women who have been sent from Nauru with serious illnesses and injuries, but they have not yet been treated.

“Everybody here is sick, they say we are sent here for treatment but nothing happens, we just get worse,” one refugee from Myanmar tells the Guardian. “We just wait, for what, we don’t know. Who knows what our future will be.”