Three teenage boys are being wrongly held in the Manus Island immigration detention centre alongside adult men because of rushed assessments, Amnesty International claims.
The human rights organisation visited the Papua New Guinea island in November and released a report on Wednesday describing the facilities as a cross between a prison and military camp.
The report says 1100 male asylum seekers live in three overcrowded compounds that lack privacy and provide no shelter from tropical heat.
Amnesty International claims the immigration department is rushing age determination assessments since the introduction of a new rule that asylum seekers must be transferred to PNG within 48 hours of arriving on Christmas Island.
Amnesty International interviewed three asylum seekers who claim they're aged between 15 and 17 and are being housed in conditions that are "traumatising for people their age".
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Age determination interviews on Manus Island are carried out by teleconference with officers in Australia, the report said.
The report said asylum seekers spend several hours a day queueing in the blistering sun for meals.
Detainees spoke of verbal and physical abuse from detention centre staff who refer to the asylum seekers by their boat identification numbers, Amnesty International said.
The report was scathing of the hangar-like accommodation called P dorm which it says violates the UN convention against torture.
"Asylum seekers reported finding snakes in the room and flooding when it rained," Amnesty International spokesman Graeme McGregor said.
"It has a corrugated roof, no windows and only two small working fans to be shared between 112 men in overcrowded conditions."
It said the food on offer often contained flies and worms and one asylum seeker found a human tooth in his meal.
It said medical facilities were inadequate, people needing tests or specialist treatment in Port Moresby or Australia had been refused access and their health was deteriorating.
Amnesty International also raised concerns about the welfare of gay asylum seekers in detention on the island with reports some are experiencing harassment.
It's also concerned about the lack of refugee claim processing.
The report comes in the wake of PNG foreign minister Rimbink Pato's rejection of claims the centre on Manus Island is substandard.
