Prime Minister Helen Clark has issued a personal plea for all children to be kept safe, saying she is worried by the levels of child abuse.

She used Labour's annual conference in Christchurch at the weekend to deliver one of her strongest messages against physical violence and said abusers should not be able to hide behind a law letting parents use "reasonable force".

"I am left troubled by the level of abuse, violence and neglect affecting children in our country," she told delegates.

"I for one cannot accept that it is fair and reasonable for the law to allow a defence for those who assault children. That does not yet seem to be a widely accepted view in New Zealand.

"I do ask our fellow citizens to reflect on the extent to which that law is shielding and protecting those who are violent."

Helen Clark said the case of a Hamilton man who was acquitted of assault after using a rubber hose to beat his daughter, leaving her with a raised 15cm-long lump on her back, had set a benchmark for "reasonable force" that was unacceptable.

She said entrenched views on physical discipline might get in the way of protecting some children.

The Prime Minister has consistently said that Labour does not intend to ban smacking.

However, she wants the law changed to remove a defence of "reasonable force".

She said such a defence could not be used by an adult accused of assaulting another adult, and it should not be available to adults who hurt children.

The Government is about to embark on an education campaign for parents on disciplining children. A law change is not planned until that is finished in two years.

Helen Clark told the Herald the public was not yet linking a tolerance of physical violence with child abuse.

"I'm just staking it out there as something I feel personally rather strongly about."

She said any debate about policies for preventing child abuse would also now be held against the backdrop of the troubled Child, Youth and Family Services.

The Government last month announced a $127 million bailout for the department after a damning review said it was in crisis, with demoralised staff and unable to protect many children on its books.

Labour emphasised its social policy roots at its annual conference, which attracted almost 700 contented delegates, but while there were hints about new spending, no specific promises were detailed.