Hugh Pavletich, one of the report’s authors, said housing had become more affordable in Australia over the past year as prices fell amid tightening credit. He said that Ms. Ardern’s government, which took office in October 2017, had been “messing around” by focusing too much on the hotly debated plan to build 100,000 more houses — called KiwiBuild — instead of freeing up more land for construction, which he said could have kept prices in check.

“If they’d got out of the starting blocks with structural reforms centered around land supply and infrastructure financing soon after the election, it would have sent a far clearer signal to the market and subdued it significantly as these changes were put in place,” he said.

But the center-left Labour Party that Ms. Ardern leads has now conceded that its flagship policy will not ease the housing crisis as rapidly as it had hoped. The prime minister told reporters Wednesday that the government would still build 100,000 housing units in a decade, but that its interim targets would be scrapped.

The government now expects to have 300 new homes built under the plan by July, rather than the original plan for 1,000.

Phil Twyford, the housing minister, said Wednesday that there would be a “recalibration” of the policy, noting that demand for the new homes in some areas had been weaker than expected. KiwiBuild has faced criticism from political opponents that even its cheapest houses are too expensive for first-time buyers who had been shut out of the market.