The Corrections Department is blaming conditions in the construction industry for a six-month delay in introducing new modular units to prisons.
The units are being built in China and the first batch, which was announced in 2017, is now unlikely to be operational until later this year.
At a Justice Select Committee meeting, Corrections' deputy chief executive Jeremy Lightfoot said the organisation was happy with the progress being made on the pre-built units.
He said the majority of them have now been shipped to New Zealand, and while one shipment was damaged in stormy weather, repairs have been made and there were no problems with rusting in the units which have arrived.
"We spent a lot of time and effort making sure that we understand the quality of the shipments that are leaving China so that we are confident when they arrive in New Zealand that they're going to meet our quality standards.
"When we then do inspections and pick up damage caused in transit, we have very good recourse to make sure those are remedied."
Mr Lightfoot said the six-month delay in putting up the units had come as a result of the tight conditions in New Zealand's construction environment.
"When you have complex sites, when you have lots of sub-contract supply chain elements to manage, and you've got ground conditions you need to work through, there will be complexities.
"These projects were commissioned under reasonably tight time frames and our partner has done very well in managing these challenges."
However, National's Corrections spokesperson David Bennett said he believed there had been wider problems.
"They're continually trying to change them to make them best practice. That shows that the original designs weren't up to speed and there seems to be trip after trip back to China to try and investigate and see what's going on with these buildings.
"They look like they're a temporary solution."
On the other hand, it was also suggested at the select committee that the modular units could be used to replace some of Corrections' older prison stock.
Chief Custodial Officer Neil Beales said a significant drop in the prison population in the last year had given them the opportunity to look at a wider use of the modular units.
"What that now allows us to do is continue with this programme, but explore what other options might be available to us in the future.
"[We can] look at potential areas of our current estate that we might be able to look at mothballing, or re-purpose."
However, Mr Bennett said he was also sceptical about that.
"They were only seen as a temporary addition for any increase in prison population," he said.
"Now for the department to be saying that they're going to be a long-term replacement for existing stock that might be getting old and needing replacement ... doesn't make much sense."
The Corrections Association, the prison officers' union, also said he had concerns about the delays in implementing the modular units.
Its president, Alan Whitley, said he believed Corrections would have been better off sticking to traditional prison-building methods.
"I actually don't think there's any benefits to it to be perfectly honest," Mr Whitley said.
"I've seen standard 60-bed units built in a lot less time than they've managed to build these, considering that they're going to be housing low-security prisoners in them.
"They'd be far better off sticking with the standard construction method by the look of it; for a low-security unit you can get one of those up inside a year."
The second group of modular units signed off in last year's budget will now not be ready for use until early next year.