Without fresh water or power, they are drinking rainwater from rubbish bins and eating one meal a day or less to preserve their dwindling food supplies.
The sewage system is blocked, so the toilets don't flush and disease is spreading.
Amnesty International says about 90 men have fallen sick, three of them seriously.
Yet a political resolution looks unlikely, despite widespread criticism. Australia is heavily committed to using these offshore prison camps as a deterrent for asylum seekers who have been coming in their thousands on overcrowded boats, mainly from the Middle East via people smugglers in Indonesia.
It claims the so-called boat people are taking the place of legitimate refugees and encouraging a criminal trade, but this argument ignores the messy reality of refugees' lives.
Almost 90 per cent of the assessed asylum seekers on Manus Island - who come mainly from Iran, Afghanistan, Pakistan and Iraq - qualify as genuine refugees. They may have paid for a boat place, but most people in their circumstances would probably do the same.
Australia could probably absorb their numbers within its generous refugee intake of 18,000 a year (far more than New Zealand, it must be said) but the real sticking point is border control.
Our northern neighbour has a longstanding fear of an Asian invasion, which is now coupled with fear of terrorism and radical Islam.
Politicians from both major parties are unmoved by the global condemnation, because the policy is popular with most voters, who don't want thousands of these refugees in their country. Offshore detention has also proved brutally effective.
When Labor briefly scrapped it in 2009 the annual number of boat people soared from 25 to 17,000 in 2012, prompting Kevin Rudd to reach for the Manus Island solution.
New Zealand is already getting blowback for its efforts. An unsubtle leak this week suggested Australia had intercepted boats coming our way and there will always be fears of reprisals on trade or government services for New Zealanders living in Australia.
But so far Ardern is playing it right. Her relentlessly positive focus has been on tackling the "human face of the problem", while tiptoeing around the implications of alleged human rights abuses by our closest ally and neighbour.
