Australian Prime Minister Scott Morrison issued a national apology to thousands of victims of institutional sex abuse yesterday, admitting the state utterly failed to stop "evil, dark crimes" committed over decades.

"This was done by Australians to Australians, enemies in our midst, enemies in our midst," Morrison said in an emotional address to parliament, designed as a belated apology to the 15,000 known survivors of child abuse.

"As a nation, we failed them, we forsook them, and that will always be our shame," he said, recounting abuse that a government inquiry has shown was rife in schools, churches, orphanages, sports clubs and other institutions across the country over decades.

Morrison's voice cracked and trailed off as he recounted a history of exploitation, cover-ups and state failure. He declared a new national credo for future allegations: "We believe you."

The state apology comes after a five-year Royal Commission that detailed harrowing child sex abuse claims involving once well-trusted institutions.

"Today, we say sorry, to the children we failed. Sorry. To the parents whose trust was betrayed and who have struggled to pick up the pieces. Sorry. To the whistleblowers, who we did not listen to. Sorry," Morrison said.

"To the spouses, partners, wives, husbands, children, who have dealt with the consequences of the abuse, cover-ups and obstruction. Sorry. To generations past and present. Sorry."

In parliament, lawmakers stood for a moment of silence following the remarks, as hundreds of survivors looked on or watched in official events across the country.

Normal parliamentary business, a session of prime minister's questions, was suspended in a bipartisan show of respect.

Outside the parliamentary chamber, relatives of victims wore tags with the names of departed daughters and sons, brothers and sisters, for whom the apology came too late.

After meeting some of the victims, Morrison told journalists "I've never felt such pain in one room, ever."