Refugees detained in Nauru and Papua New Guinea's Manus Island are suing the Australian government for torture and crimes against humanity.

Photo: Behrouz Boochani

The non profit National Justice Project today filed two class actions in the High Court covering about 1200 people remaining in Nauru and Manus.

The actions allege the refugees have been subjected to intentional harm, severe deprivation of physical liberty and inadequate conditions.

To be led by Julian Burnside QC, the actions also claim the refugees were arbitrarily imprisoned and denied access to proper medical assessment and treatment.

Both are seeking injunctions to stop the alleged breaches of Australia's duty of care as well as damages.

Lawyer George Newhouse from the National Justice Project said there was plenty of evidence.

"We've seen it in the cases of the children that we've had to rush to court to have moved to Australia for medical treatment," Professor Newhouse said.

"We've seen it in the people that have died offshore. There are 12 people that died offshore because of the way they've been treated by the Australian government."

In 2017, the Australian government agreed to pay $AU70 million in compensation to Manus Island refugees for holding them in conditions that caused them physical and psychological harm.

In October, the PNG Supreme Court dismissed a case brought by 731 Manus refugees that sought compensation for unlawful detention.