SYDNEY (AFP) - Self-harm by asylum-seekers being held at Australia's offshore detention centres takes place on average once every two days, a report said on Saturday (Jan 16), with some prospective refugees swallowing poison, cutting themselves and attempting suicide.

Under Canberra's hardline immigration policy, Australia sends asylum-seekers that attempt to arrive by boat to the Pacific islands of Papua New Guinea and Nauru for processing.

They are barred from being resettled in Australia even if found to be refugees.

The Fairfax Media report, using Immigration Department logs obtained through Freedom of Information laws, found there were 188 self-harm incidents involving asylum seekers in Nauru in the 12 months to July 2015.

Self-harm incidents at the Manus Island camp on PNG numbered 55 for the same period.

An immigration department spokesman said the number of self-harm incidents at the two offshore camps "have reduced considerably in recent months".

"Where an individual in a regional processing centre threatens self-harm or actually self-harms they are immediately provided with both counselling and medical services," the spokesman added in a statement on Saturday (Jan 16).

"The services provided in both Nauru and Papua New Guinea are broadly comparable with health services available within the Australian community."

The incidents reported included asylum-seekers stuffing tea bags down their throats, attempting to hang themselves by bedsheets or other makeshift nooses, and a woman who "poured boiling water over (her) lower limbs", the report said.

Self-harm cases in the onshore detention network, which include people held for breaking immigration laws and asylum-seekers living in the community, stood at 706 over the same 12-month period.

A total of 1,459 asylum-seekers were being held on Manus Island and Nauru at the end of 2015, according to immigration figures.

Some 28,919 people are under detention or live in the community within the onshore detention network, the figures show.

A Senate inquiry into the Nauru facility last year found that conditions were inadequate and unsafe, with submissions to the hearing including allegations of rape and other abuse.

Human rights groups have criticised the policy against asylum-seekers arriving by boat and the detention conditions, but the Australian government has argued the harsh measures have helped stop people dying at sea.