More than 40,000 children across Australia cannot live safely at home and that number is increasing, a national inquiry has been told.

The children are placed in out-of-home care where a significant number suffer sexual, emotional or physical abuse, the Royal Commission into Institutional Responses to Child Sexual Abuse has heard.

Gail Furness SC, counsel advising the commission, said the children were coming into care at a younger age and staying longer with foster carers, relatives or in group homes.

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Ms Furness said gaps and inconsistencies in data collection by states, territories and charitable organisations means that in many cases the abuse remains hidden and the children unsupported.

The delivery of out-of-home care services varies across jurisdictions.

In Victoria they have been totally handed over to non-government organisations.

NSW is committed to doing the same thing and currently just more than half of all children in statutory care in the state are with agencies like Barnardos, UnitingCare CatholicCare or family services charities, Ms Furness said.

She said while the protection of children at risk is a state and territory responsibility, valid national data are not readily available.

According to one set of statistics 43,009 children were in out-of-home care as of June 30 2014 with 51,557 children in at least one care placement during the 2013-2014 financial year.

Ms Furness said the average nationally was 8.1 children in care per 1,000 children aged 0 to 17 in the general population.

This number increased significantly when it came to indigenous children.

According to the 2015 report on government services, nationally there were 51.4 indigenous children in out-of-home care for every 1000 indigenous children in the population.

“The rate of indigenous children in out-of-home care was approximately nine times the rate of non-indigenous children”, Ms Furness said.

She said there was no national body collecting or publishing statistics on the number of children in out-of-home care, or collecting and publishing statistics on the number of children in care who were sexually abused, or the outcomes of any investigation of those allegations.

There was some data available this year on attempts to measure whether children in out-of-home care had been, or were likely to be “abused, neglected or otherwise harmed”.

Data was not available for NSW or Victoria but Queensland reported that 3.7 per cent of children in care in 2011-2012 suffered abuse or neglect.

That number decreased in subsequent years.

There were 8,185 in out-of-home care in Queensland as of June 30 2014.