Sydney is one of the least affordable places to buy a home, an international survey has found - and its authors say government land release policies bear a large part of the blame.

The harbour city placed second only to Vancouver on a list of the world's most expensive residential markets compiled by the Demographia International Housing Affordability Survey of 272 markets in six countries.

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Melbourne and Adelaide were not far behind - ranked third and fourth in the list of least affordable major cities, above London, New York and San Francisco.

As a result, Australia was by far the least affordable of the countries surveyed, followed by New Zealand, Britain, Canada, Ireland and the United States.