National leader Simon Bridges has announced a National Government would introduce a new offence to criminalise the non-disclosure of information relating to child abuse cases.

The National Party and ACT want to make knowing about child abuse but failing to report it a criminal offence, punishable by three years in prison.

It follows a call from Children's Commissioner Andrew Becroft this week for the 'right to silence' to be abolished or amended in cases of child abuse.

The push for new laws comes after a case of a four-year-old boy from Flaxmere who was critically injured in a suspected case of child abuse.

The boy - who will likely be permanently brain damaged if he survives - was admitted to hospital late last month, after police were called to a family violence incident at a property in Ramsey Cres, where they found him badly bruised and suffering from a severe head injury.

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Opposition Leader Simon Bridges said that under National, the new offence would have a maximum penalty of three years in prison.

ROSS GIBLIN/STUFF Minister of Justice Andrew Little said unless draconian measures were introduced, to compel people to talk, he was unsure how effective a new law could be.

The law would require someone to give police information unless they had a reasonable excuse not to.

It would be similar to a 'Failure to Disclose' offence introduced in the Australian state of Victoria in 2014 for child sex abuse cases, he said.

Bridges, a former Crown Prosecutor, told assembled media that he understood the issues, having prosecuted harrowing cases involving child abuse.

"I can't stand by and watch stories in the news about children being killed and injured where nobody is held to account."

"There are more that should have come to me to prosecute but they never made it to court because those involved refused to tell police what had happened. Those children never got the justice they deserved," he said.

Prime Minister Jacinda Ardern said the National Party's previous changes to child abuse laws had not worked but the issue did need to be looked at.

ACT Deputy Leader Beth Houlbrooke said if elected, she would submit a bill into the members' ballot that would include up to two years' imprisonment for a person who fails to answer reasonable police questions after a child had sustained serious non-accidental injuries.

The Justice Minister had failed to recognise that there were already various exceptions to the right to silence in the law, she said.

Abigail Dougherty/STUFF ACT Deputy Leader Beth Houlbrooke said if she was elected, she would enter a bill into the members’ ballot to create an offence for failing to cooperate with police investigating a case of child abuse.

"Little needs to explain why fisheries and customs officers, and even liquidators, can demand information from people, but police investigating child abuse cannot."

"If it's good enough for fisheries officers, it's good enough for police investigating the abuse of a four-year-old in Flaxmere."

But Justice Minister Andrew Little, who ruled out changing the law, questioned how it could make a difference and not encroach on the Bill of Rights Act.

Unless draconian measures were introduced to compel people to talk, he was unsure how effective a new law could be.

Any new powers could be used outside of the context they may be intended and affect innocent people, he said.

"We ought to be concerned about family members who so far lack the courage to speak and do what is right for the sake of justice …. but when we write laws we have to think about the broader impact on other people."

He had asked the Ministry of Justice for advice on changing the police caution - to front up what they knew at the point of arrest or interview - which he believed would be a better balance.

Little suggested following the British rule that warns a person they have a right to silence but if they chose not to say something but later relied on it in court, they might not get that opportunity.

He urged anyone who knew anything, even on the days leading up to the hospitalisation of the boy, to come forward.

"Somebody knows something and they have a human, moral duty, to have the courage to speak up - however difficult that might be for them personally."