A Melbourne law firm has launched class action against Immigration Minister Scott Morrison and his department on behalf of a six-year-old girl held in detention on Christmas Island.

The case would accuse the Commonwealth of breaching its duty of care by failing to provide adequate health care for asylum seekers and not enrolling children in school.

Maurice Blackburn lawyer Jacob Varghese said the class action would also cover any asylum seeker injured or pregnant on Christmas Island in the past three years.

"At the end of last month, there were 334 people on Christmas Island and 148 children, the class action covers people who have been on Christmas Island for the last three years, so that number would be in the thousands of potential claimants," Mr Varghese said.

Lawyer Katie Robertson said the lead plaintiff, who could not be identified, was a six-year-old girl known as "AS" who has been detention for over a year.

"She's suffering from both physical and mental health issues. She's experienced an ongoing dental infection that was ongoing for three months," Ms Robertson said.

"She also suffers from separation anxiety that arose as a result of her mother being transferred to the mainland shortly after she arrived in Australia with her parents.

"They were separated in that time, and in that time she has developed bed-wetting and stammering."

Ms Robertson said the girl has been on the waiting list to see a specialist for her stammer for over a year now.

She said the six-year-old has been diagnosed with post-traumatic disorder, and an alternative diagnosis of major depression and anxiety.

"When I met with her about a month ago, she struck me as an extremely sad and disturbed child," she said.

A spokesperson for the Minister for Immigration and Border Protection said Mr Morrison would not comment on the case.

"The Minister notes a claim was filed today by Maurice Blackburn. As this matter is before the court, it would not be appropriate to comment further," the spokesperson said in a statement.

Suing to have people taken off Christmas Island, compensation

Mr Varghese said the firm was suing for compensation and an order that people be taken off Christmas Island and placed in community detention.

"We say that the Minister and the Department [of Immigration] owe a duty of care to people who are detained on Christmas island," he said.

"By failing to provide adequate health care and a variety of other circumstances including not enrolling children in school and detaining children other than as a last resort, the Commonwealth is breaching that duty of care."

Mr Varghese said it was too early to say what level of compensation would be sought.

"I think there's going to need to be a serious process of assessing how deep the damage runs really," he said.

"We know that there are lots of people with serious health issues on Christmas Island and part of the process of the class action will be taking a view on how many people are affected, and what kind of compensation can help put things back again."

Greens support class action

The Greens said the class action showed why asylum seekers should be released into the community.

The Greens' immigration spokeswoman, Sarah Hanson-Young, said children were being damaged every day in detention.

"This compensation case before the court is unnecessary if the Government was to treat people properly," Ms Hanson-Young said.

"To look after the children in the way they deserve to be looked after. To treat children with care, with dignity."