The Salvation Army says a shortfall of at least 2500 houses in Auckland is hitting areas already struggling to cope.
It says building consents in the city have fallen 22% in the past year and the rate of building is not keeping up with population growth.
Figures from Statistics New Zealand released last week show building consents at their lowest since 1983.
Salvation Army social policy director Major Campbell Roberts says the shortage seems to be affecting only Auckland - but it could worsen, leading to increased housing costs and overcrowding.
The Monte Cecilia Housing Trust, which provides emergency housing for families, says the organisation is fielding about 60 calls a month.
The Construction Industry Council says its own evidence supports the Salvation Army's findings.