Rights groups Amnesty International and Human Rights Watch have conducted a joint covert investigation with two of their representatives spending 12 days on the island last month.
The report claims detainees are routinely neglected and sometimes denied medical care and are subject to abuse and violence from Nauruans.
Amnesty International says it had tried numerous times and failed to get permission to visit Nauru but one of its staff managed to travel there legally to see the conditions for herself.
Amnesty's Doctor Anna Neistat says what she saw appalled her.
"Quite honestly, I can tell you that that I've been covering war zones and closed countries for the last 15 years and the situation on Nauru stands out, it does stand out because of almost senseless cruelty and injustice that is happening there."
Doctor Neistat and a representative from Human Rights Watch, Michael Bochenek, interviewed 84 asylum seekers and refugees and four service providers.
Michael Bochenek told the ABC all the detainees complained of mistreatment by the Nauruans.
"I had people tell us that every time they ventured out into the community, they are at least verbally harassed, sworn at, cursed, spit upon, have bottles thrown at them and other objects. People have described been swerved at as they walked down the side of the road and we have much more serious physical attacks. People attacking with pipes, with sticks, drawing blood, and when refugees and asylum seekers complain to police about the actions of people in the local community those complaints are very often met with no response whatsoever."
This detainee says she and her family totally misjudged Australia.
"We chose Australia because at least we thought it's a first world country and it supports women and children's rights but I think we were just wrong. I mean they've tortured us for three years now."
She says being on Nauru has almost robbed her of the will to live.
"I would much rather die in the ocean than stay here and die daily by seeing my mum breaking down and see how she tried to hold up together. I mean it's hard."
Amnesty's Anna Neistat claims detainees are neglected and sometimes denied medical care.
She says while the detention centre is an open facility, Nauru is tiny and Australia is breaching international law by subjecting people to indefinite detention.
"The island is 21 square kilometres so it's smaller than some of the prisons in the US for example so I think the comparison is valid, so this indefinite detention of refugees and asylum seekers is also totally against international law and the fact that people have no safety and are being deprived of their most essential human rights also speaks to the fact that Australia is in breach of its international obligations."
The Department of Immigration says it wasn't consulted by Amnesty before the report was released and strongly encourages the organisation to make contact before airing allegations of this kind.
The Department says it strongly refutes many of the allegations in the report but it doesn't specify which ones.
