A doctor who worked at the immigration centre on Manus Island says he informed authorities that the facility was inappropriate for children well before they were sent there, but nothing was done about it.

ABC1's Four Corners program has gained significant access to the centre and spoken with a number of staff.

Among them is Dr John Vallentine, who worked at the centre between November and December last year.

He says the facility is "too remote" and under-resourced to safely house children and that the health clinic has "very little in the way of paediatric equipment".

Despite this, 30 children are now housed on the island, which is a few hundred kilometres north of the Papua New Guinea mainland, near the equator.

Dr Vallentine says he told his employer, International Health and Medical Services (IHMS), of his concerns five months ago.

"The whole time I was there it was just a disaster, medically," he told Four Corners.

"Almost from the day I arrived it was obvious to me that it was not a clinic that would work in its current state.

"From early on I was sending lists both through my health services manager up there and directly to the medical staff of IHMS in Sydney saying, 'look, we desperately need this stuff'.

"Stuff being oxygen, antibiotics, bladder catheters, suckers, tracheotomy equipment, anaesthetic agents, sedatives, morphine, ketamine, and these things didn't arrive.

"For the first time in my life I felt ashamed to be an Australian, up there seeing this squandering of money.

"It's just a remote, silly place to be putting people."

The ABC gained access to Manus Island and obtained footage with hidden cameras. ( Four Corners )

IHMS is paid $2.5 million a month by the Australian Government to provide health services to the offshore centres in Nauru and Manus Island.

It is responsible for health checks on asylum seekers selected by the Department of Immigration for offshore transfer.

Dr Vallentine says his concerns "turned to alarm" when the children, including an anaphylactic boy and a girl with a history of needing blood transfusions, arrived at the centre.

"The thing about children from a medical point of view is that they get sick very quickly," he said.

"You don't have nearly the same luxury of time to sort things out and the problem, or one of the problems at Manus Island is its remoteness.

"Worst of all, this established 24-hour delay, between calling for a medical evacuation by air and the plane arriving and getting the sick person out, is just too long for kids.

"So I was worried about children being there at all I must say."

The Salvation Army has a $75 million contract with the Australian Government to work with asylum seekers on Manus Island and Nauru.

Major Paul Moulds was so disturbed by what he had seen that he decided to speak to Four Corners.

"I've had some hard days and I've seen some pretty difficult things in that role, but I don't think I've ever had a harder job as what this called for as we work with asylum seekers on Manus and Nauru," he said.

"I can say quite honestly the people I work with from government and from the host countries, I don't think they want to injure asylum seekers.

"But Australia has to... weigh up the consequences of what it's doing.

"It has to think deeply, and I hope there is a really reasoned and logical and intelligent debate about this policy."

Manus Island has been described as a "remote, silly place to be putting people". ( Four Corners )

Australian Human Rights Commission president Gillian Triggs has not been to either Manus Island or Nauru.

She says the solicitor-general told her she has no jurisdiction outside Australia.

"This is a curious phenomenon," Ms Trigg told Four Corners.

"What is absolutely crystal clear as a matter of international law is that Australia is responsible for the lives and wellbeing and legal rights of these people, and as human rights law is at the core of my job, I would have thought it appropriate that I be invited to go there and to make some kind of visit to the people concerned."

Another former Manus employee describes the camp as "stressful", with only a fence between the children and families and nearly 200 single men.

Morale among the men, who have spent five months in tents, is low and centre workers describe frequent suicide attempts and self-harm incidents.

While some processing has begun in Nauru, there is currently no proposal as to how and when asylum seekers' claims might be assessed on Manus Island.

Workers with first-hand experience of both Nauru and Manus Island have told Four Corners that much of the distress among those detained in the centres is the unfairness of the system.

Although almost 700 asylum seekers have been transferred offshore, thousands of others who arrived over the same period were sent to Australia and have been released with bridging visas.

A spokesperson for the Immigration Department said the facilities were adequate, describing them as "comparable with Australian standards".

But in a submission to a parliamentary inquiry last month, the department said conditions were cramped and problematic.

It said there was no reliable power supply, limited drinking water, and the conditions for inmates increased the risk of mental health problems.

Immigration Minister Brendan O'Connor is yet to comment on the claims raised in the program.

For more on this story, watch Four Corners' No Advantage on ABC iview.