New Zealanders on Christmas Island are being left to rot in a cesspit of misery, according to Labour MP Kelvin Davis.

Photo: AAP

Mr Davis met eight detainees during a visit to Australia's immigration detention centre on the island.

"They've basically almost given up hope - the feeling of despair is palpable, so really they're just rotting away in a cesspit of misery."

The centre houses non-citizens, including 72 New Zealanders, who have served more than a year in jail and who are liable for deportation under tougher visa laws Australia enacted last year.

Mr Davis wrote to Australian Prime Minister Malcolm Turnbull saying the centre breached the human rights of New Zealand detainees, all of whom felt desperate and hopeless.

He said he had asked to visit a ninth inmate but was refused, and he believed that was because the man had been injured in an assault by prison guards.

Photo: RNZ / Alexander Robertson

Mr Davis has previously described the conditions as terrible, and said the inmates did not receive enough food and that medical attention was inadequate.