Australian Institute of Health and Welfare data released on Friday showed a more than 300 per cent rise in known carer adoptions in the decade leading up to 2018-19.

It's something institute spokeswoman Louise York said was down to a desire by carers to "provide permanency for children in out-of-home or foster care environments".

Despite the huge rise in known carer adoptions over the 10 years, total adoption rates between 2017-18 to 2018-19 dipped from 330 to 310.

Of the 310 adoptions in Australia in 2018-19, 54 per cent being male and most being adopted by married couples.

There were 142 known carer adoptions last financial year, with the new parents tending to be older than other Australians who adopted.

"This rise has been driven by NSW where recent reforms have increased the focus on adoptions by known carers," Ms York said.

These children also tended to be older and male, with more than half of known child adoptees older than 10.

Nearly all of local adoptees, that is children who are legally placed for adoption but with no previous contact with their adoptive parents, were aged five or under.

The institute said a falling rate of local child adoptions could be pinned on Australia's changing views and social trends, like falling fertility rates, birth control and an increase in support for single parents.

Known carer adoptions tended to involve people in their mid-40s to 50s, while slightly younger families - in their early-40s - adopted from overseas.

Most adoptions were for Australian children, with only 57 being from other countries as processing times for inter-country adoptions plummeted.

But Ms York said this still differed country by country, with adoptions from Taiwan taking up to four years while South Korean adoptions took up to 21 months.

There were 12 Aboriginal and Torres Strait Islander children adopted in 2018-19, a 25-year high, with all having pre-existing relationships with the adoptive parents.

Australian Associated Press