Detention conditions harsh: Hanson-Young

No grass, no play area, no sign of improvement.

Conditions are dire on Christmas Island where hundreds of asylum seeker children and their families remain in long-term detention.

That's the view of Australian Greens Senator Sarah Hanson-Young who has spent four days on the small island northwest of Australia.

"It is fair to say that the conditions in these compounds are probably the worst I have seen them," the South Australian senator told AAP from the island on Tuesday.

It is about a year since she has visited the four detention facilities which include a main compound and three smaller areas for families and children.

"At two of the family compounds, `lilac' and `aqua', there are extremely harsh conditions," Senator Hanson-Young said.

"When I was here three years ago I was told these were only temporary facilities, but they're still operating, they're crowded with very young children and their families."

Of particular concern to the senator was the number of pregnant women in detention, some who came to the island as expectant mothers.

"Over the next six months there are going to be over 100 babies born," Senator Hanson-Young said.

"(The newborns) are going to spend their childhoods detained, imprisoned and knowing no different."

There is no independent oversight of the health services available on the island and no child psychologist, Senator Hanson-Young said.

"Medical experts agree and the staff here tell me that six months is the critical time (in detention), after that people start to deteriorate and there's not the mental health support mechanisms in place.

"Twelve months ago people were getting moved through the system quickly but now it is government policy that these people will remain in detention indefinitely and I don't see how we are going to save these children from more damage."

Senator Hanson-Young has spoken to scores of men, women and children during her visit.

"Every one of them had a story about genuinely fearing for their life which had led them to leave their home country," she said.

One Syrian boy said he was stepping over dead bodies outside his home on his way to school after a string of bombings in his neighbourhood.

Two 17-year-old Somali girls sought asylum after militia killed their families and then planned to marry the teens.

"There is no escaping the fact that this policy (of detaining asylum seekers) is creating the next damaged generation," Senator Hanson-Young said.

She plans to share her concerns with the Australian public and parliament after returning home on Tuesday night.