New Zealand is already working to change the state care system, and an inquiry into child abuse will only distract from that, opposition leader Bill English says.
Many of the thousands of children placed in state care between the 1950s and 1980s were subjected to sexual, physical and mental abuse.
Prime Minister Jacinda Ardern promised an inquiry would be launched in Labour's first 100 days, but there have been calls to broaden the government's inquiry into the abuse of children in state care.
Ms Ardern rejected that, saying the focus should stay on the role the state played.
Speaking to Summer Report for the first time this year, Mr English said he had not changed from his government's position that there was no need for a historical inquiry.
"An inquiry that's launched now in my view frankly is likely to take the energy that's currently been directed to positive change, so these things do not happen again and direct it into going over ground that has been gone over," he said.
"The previous government had a very hard look at how state care was working, went through a process in great detail, and now there's a major change going on in the operations of state care based on all the analysis of all the past performance and on principles of social investment so we can do a much better job for these young people."
The United Nations recommended in August that New Zealand hold an independent inquiry into the abuse of children and adults with disabilities in state care.
"The inquiries in Australia and the UK ... they've been Royal Commission type inquiries not really focused on changing the machinery of government, based simply on listening to the stories.
"Now, in New Zealand there's been a parallel process going back quite a number of years through the confidential listening process, and a large number of legal settlements regarding abuse, and that has provided the opportunity for people to be heard."
"So in that sense the ground has been covered in a couple of different ways," he said.
He also said he had heard some of the stories first hand.
"As an MP I've had the experience I'm sure many other local MPs have had, of sitting in the office and hearing these stories.
"In fact, I remember them going back to the early '90s, hearing some of the horrific stories out of the mental health institutions at the time, which certainly persuaded me that those needed to at least change and probably be closed."
"One of the benefits of the processes that have been gone through is that victims get to tell their story."
Mr English also criticised the government's 100-day plan, saying although it had done most of what it set out to, it achieved little.
"The question is whether the checklist is compiled of things that are going to make any difference to anybody."
"Setting up the mental health commission doesn't change any mental health services, setting up the child abuse inquiry if anything may detract from the scale of change that's going on there right now.
"The free first year of tertiary education ... is being explained to us in Parliament as MPs didn't need $100,000 a year, well in my case they've handed my household $600,000 a year.
"Its' a very expensive, very poorly targeted policy that will have the effect of getting maybe a few thousand, couple thousand more people into tertiary education.
He said New Zealand was doing well, and his opposition would criticise the government where it seemed to be going "off track".
"When you've got an economy generating so many jobs, you've got strong government books that allow us to deal with child poverty, you've got well-developed policy that's allowing us to fix the quality of fresh water in New Zealand - then keeping that momentum going is important."
"If the government says they can do better then we'll encourage them and support them where they have policy that says they actually will do better.
He also targeted the coalition arrangement.
"The question is going to be will they agree on anything past that 100 days."