Children being held in immigration detention on Christmas Island have told a Human Rights Commission inquiry it is like "hell" in the centre.

After struggling to get information from the Immigration Department about the wellbeing of children in detention, the commission launched a national inquiry into the matter.

That gives it significant powers, including access to detention centres.

The commission has just held its first visit to a detention centre as part of the inquiry, spending a week on Christmas Island.

Its president Gillian Triggs says the children there told them the place was "hell".

"The overwhelming sense is of the enormous anxiety, depression, mental illness but particularly developmental retardation," she said.

"The children are stopping talking. You can see a little girl comes up to you and she is just staring at you but won't communicate."

Professor Triggs says most of the 315 children who were there had been detained for between six to eight months.

She says many of the drawings the children gave them depicted prisons.

"These children are actually identifying themselves by their numbers, not by their names, which is shocking in itself," she said.

"This is a very typical picture where they are asking for freedom.

"They're asking for help and they perceive themselves as being behind bars and in prison. And this theme is repeated over and over again."

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Listen Duration: 5 minutes 8 seconds 5 m Human Rights Commission says enormous anxiety among children on Christmas Island ( Lexi Metherell ) Download 2.4 MB

Professor Triggs describes the conditions at Christmas Island as inhumane.

"To state the objective principles of law as a matter of very clear international law: children should not be detained for anything more than what is absolutely necessary for health checks and security checks," she said.

"These children are being detained on what are, on any analysis, prisons at a remote island in shockingly hot, humid and difficult circumstances, in a way that cannot meet what you would imagine would be the standard at an international level."

Opposition immigration spokesman Richard Marles says the reports are "concerning".

"I think it is important that these inquiries are being undertaken. And I think those reports are concerning about the state of children at Christmas Island," he said.

PNG judge probes Manus Island centre

In Papua New Guinea, there is also a push to inquire into conditions in detention.

A judge of the PNG National Court, David Cannings, launched a judicial inquiry into the Manus Island detention centre three weeks ago.

Daniel Webb from the Human Rights Law Centre says the inquiry "takes the legal system to asylum seekers".

The PNG government has fought the inquiry and on Friday the higher Supreme Court issued a stay on it.

Justice Cannings responded by establishing a second inquiry.

"The first inquiry was initiated by the court and the court took it on notice that there were human rights concerns about what was happening on Manus. That's the inquiry that has been temporarily adjourned," Mr Webb said.

"The second inquiry relates to information that was specifically presented to the court by the lawyer for 75 asylum seekers on Manus.

"And the court has received that information and used it to commence a second inquiry."

Mr Webb says the National Court is "incredibly powerful", but says it is hard to speculate if it could shut down the Manus Island detention facility if it deems necessary.

"These are the superior courts of a sovereign nation and they're empowered to do all of those things that superior courts are empowered to do," he said.

The Federal Government says it has been informed by the PNG government about the Canning inquiry.

A spokesman for Immigration Minister Scott Morrison says he supports the actions the PNG government considers necessary to take upon their own initiative, within their own sovereign jurisdiction and consistent with their own constitution.

Mr Marles says transparency is the key to ensuring the centre is operating as it should.

"It's obviously important that this is a facility that is run in a way which plays its part in terms of reducing the lives lost at sea," he said.

"But it's also important that it's a facility that does provide safe, secure, humane and dignified accommodation for people who are in it.

"The best way to ensure that is transparency. We have always been concerned about the lack of transparency which has been evident in the way in which the Abbott Government has gone about managing its asylum seeker policy."