That equates to 8 per cent of the 5357 children under 18 in care, up from 5.6 per cent in 2018.
The agency says it is improving its care but has previously "acknowledged the vast improvement needed in compliance" across its social work practice.
This was noted by the Independent Children's Monitor, in its recent inaugural annual report, that found Oranga Tamariki was fully compliant just 2 per cent of the time across all 12 of its own practice requirements, and that it still lacks the data to know if it is taking proper care of children or not.
It was compliant across six or more practice requirements three-quarters of the time.
The Safety in Care report comes amid renewed controversy around the Government's proposals to overhaul oversight of the state care system - some say weaken, by reducing the Children's Commissioner's powers.
It shows:
- 289 children suffered 344 incidences of physical harm - 183 children suffered 252 incidences of emotional harm - 77 suffered 88 incidences of sexual harm - 58 cases of neglect of 34 children
Most occurred in the actual placement - such as the family or non-family home or youth residence - and a minority away from the placement, for instance, abuse by a stranger.
"Some of the harm was of a serious nature and resulted in children sustaining bruising and welts," the report said.
"Some of the children disclosed being fearful of the caregiver."
In 27 cases, staff in residences caused harm to teenagers they were restraining.
Culture, attitudes failing children - advocacy group
The children's advocacy group, Whakarongo Mai, said children were unsafe at a time when oversight of Oranga Tamariki was being eroded.
"Irrespective of the amount of plaster that people are trying to put over a gaping wound, we have a massive problem around culture and around attitudes towards the care of children in this country," chief executive Tracie Shipton told RNZ.
The report showed neglect and physical harm were on the rise for the year with emotional and sexual harm cases steady compared to the previous year.
Harm can be reported by the child or a range of others. Social workers then assess the risks and the caregiving arrangement and see to the child's needs. Abusers can be prosecuted in some cases.
The report says harm done by family caregivers decreased significantly; OT noted that last year all new caregivers began being put through a new programme advising them on how to care for children.
Children who remained at their home while under OT's care, or who returned home to the care of parents, "continues to be an area of risk" - reflecting "the adult's escalation to violence in anger".
The pandemic might be in play, and it would take a closer look at this, the agency said. "The lockdown periods experienced by tamariki in the last year may be producing additional stress within care arrangements."
The Independent Children's Monitor, set up in 2019 to gauge whether OT is meeting new national care standards (NCS), said it was impossible to know if Oranga Tamariki was on target due to the poor quality of its self-monitoring.
"Oranga Tamariki respond well when tamariki enter care; practices weaken during their time in care," it said.
"In nearly two-thirds of cases, tamariki are not visited as often as outlined in their plan. This means there may not be opportunities to continue assessing their safety, wellbeing, and health and education needs."
The agency was able to answer fewer than two-thirds of the monitor's questions.
"For example, Oranga Tamariki cannot report on tamariki and rangatahi access to health services, and whether they are informed of, and understand their rights; or whether caregivers are given appropriate training and information about the tamariki they care for."
'Lack of accountability'
Whakarongo Mai said it was "appalled by the findings and lack of accountability".
After two years of having the care standards, "a significant proportion of tamariki and rangatahi are still not getting what is set out in their care plan" and "important assessments around wellbeing, including cultural, health [physical and mental] and transition to independence are largely not being completed", Shipton said.
The monitor lacked any "real power to enforce" standards.