The number of homeless people may be three times the amount recorded in official statistics, says a public health researcher.
Researcher Kate Amore says while census figures show some 7,000 people live rough or have no permanent home, the figure is likely to be much higher.
Dr Amore says the Australian state of Victoria has a population similar to New Zealand's, and consistently reports 20,000 homeless people.
She says the hidden homeless population will present a huge problem for Government agencies if not acknowledged and better managed.
Social Development minister Paula Bennett says its plausible that 20,000 New Zealanders may be homeless, using a broader definition, and more work is needed to measure the population.
She says Government agencies and community groups must co-operate to deal with homelessness.