A senior doctor who was based on Nauru fears asylum seekers with severe medical conditions could die due to delays in accessing treatment.

Dr Nick Martin, a former surgeon lieutenant commander with the British Royal Navy, alleges that patients with breast lumps, kidney stones and neurological damage were delayed diagnostic treatments, and that severely diabetic asylum seekers held within the detention regime are at risk of going blind.

"Every clinical decision that you made was being questioned by a non-medic," Dr Martin said.

"Your expertise and your autonomy was respected in the Royal Navy but in Border Force you did absolutely feel there was a political influence on the clinical cases."

Dr Martin is the most senior official deployed on Nauru to speak publicly about Australia's offshore detention regime.

His allegations are backed by an extensive cache of leaked documents obtained as part of a joint investigation between 7.30 and BuzzFeed News.

They show that Dr Martin is not alone, with his concerns widely shared by other medical practitioners on Nauru contracted by the Australian Government.

"The people I saw in Nauru, and the state they were in after being locked up there for three or four years, to me was in a way more traumatic than anything I'd seen in Afghanistan," said Dr Martin, who also served in the Middle East and the Balkans.

What he witnessed between November 2016 and August 2017 while working as senior medical officer on Nauru shocked him.

"I feel quite ashamed to have been part of it," Dr Martin said.

"I tried my best for those patients. I kept going back to do my best for these patients but I feel I've let them all down.

"The Australian Government has certainly let them down."

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Government 'breached' evacuation deadlines

Accommodation for asylum seekers on Nauru. ( Supplied: Department of Immigration and Border Protection )

Dr Martin sets out serious allegations of medical failures by the Australian Government in its care of asylum seekers and refugees.

"If you are a brittle diabetic then you run the risk of going blind, kidney failure — you have massive cardiovascular complications," he said. "Your life span is significantly shortened."

Dr Martin remembered one man whose "eyesight was deteriorating, his health was suffering immensely". But he said "we couldn't get him the treatment he needed".

He said evacuation deadlines set by him and his staff set were frequently "reached and breached" by the Australian Government, which he holds ultimately responsible for the delays.

"These medical delays put in place are absolutely criminal," Dr Martin said.

"I hope at some point there is a big inquiry and these guys do get to have a say, because they've been put at harm and knowingly, wilfully are coming to medical harm because of the policies put in place by the Australians."

In one leaked email, dated May 2017, a health services manager on Nauru identified five serious cases where asylum seekers had been waiting for months beyond the medically recommended timeframes without treatment.

In one of those cases an asylum seeker had been waiting for 12 months for medical transfer; the recommended treatment time was one month.

"All remain symptomatic and some with symptoms worsening," the manager wrote.

The manager blamed the delays on Australian officials "not attributing and not making a decision" and said it was breaking down their relationships with patients.

18-month wait for an MRI scan

This photo from 2016 shows the Nauru hospital's emergency department. ( Supplied: Amnesty International )

Dr Martin also wrote a letter to his superiors, backed by three medial colleagues, setting out major flaws at the Nauru hospital.

He outlined shocking failures in services at the hospital, including the treatment of one refugee who received six referrals to the hospital and had been waiting 18 months for an MRI scan.

At the hospital, doctors kept no notes on the patient's case.

"If I referred a patient in Australia to a hospital where I knew that no form of clinical notes would be kept, no feedback would be given and often the referral would be lost or ignored even after repeated attempts to get the patient seen, I would expect to be up before the courts on a culpable negligence charge, along with the hospital," Dr Martin wrote in the letter.

"From a clinical perspective of duty of care we are failing our patients, by knowingly referring them to a system that does them a clinical injustice."

In a rare admission, another senior official from International Health and Medical Services (IHMS), the company which employed Dr Martin, said he had also raised issues with the Australian Government "without a satisfactory response".

He said that Australia had placed "extreme limitations" on the types of patients who could seek treatment in Australia, and charged that patients are "entirely at the mercy" of decisions by Australian Border Force officers.

'Just luck no-one died on my watch'

Sorry, this video has expired Doctor says he 'felt helpless trying to get the best for patients on Nauru'.

Nick Martin still struggles with what he saw on Nauru.

"No-one died on my watch, but really that is just through luck," he said.

He put up his hand to work there because he wanted to help.

"I went into the job wanting to do my best as a doctor," he said.

But it was also a very personal decision.

During World War II, Dr Martin's grandfather, Bernard Quin, was stationed on Nauru while the Japanese were bombing the island.

He was one of a handful of Western physicians who stayed during the raids to tend to local civilians after the Japanese invaded.

"He was beheaded by the Japanese in 1943," Dr Martin said.

"He is revered in Nauru."

Some Nauruans are named "Quin" in his honour.

"They still hold him in high regard," Dr Martin said.

"So it was good to be able to go to Nauru just as a way of, in some way, of honouring his memory."

'All transferees have access to clinically recommended care'

A refugee on Nauru who claims to have been struck on the head with a baseball bat by hooded assailants in July, 2015, receives treatment at the Nauru hospital. ( Supplied )

The Australian Government has sent more than 700 men, women and children to Nauru, and more than 1,300 men to Manus Island in Papua New Guinea, as part of Australia's immigration detention regime.

Under a deal struck with the former US President Barack Obama some refugees would be reconsidered for resettlement in the US. But President Donald Trump, who told Prime Minister Malcolm Turnbull he opposed taking in the Nauru refugees, has just announced the lowest refugee intake into the US in more than three decades.

Just 50 refugees have been resettled in the last 12 months. If resettlement continued at this rate it would take more than 35 years to resettle the refugees held by Australia on Nauru and Manus Island.

Australia's detention centre on Manus Island is also set to close today.

Refugees at that centre have been offered a chance to voluntarily relocate to Nauru, which could put an additional strain on medical services.

In a statement to 7.30 and BuzzFeed, a spokesperson for the Department of Immigration and Border Force said: