HONG KONG (BLOOMBERG) - Hong Kong retained its rank as the most expensive housing market among 406 major metropolitan regions in the annual Demographia International Housing Affordability Survey for the seventh year in a row.

The median price of a home in Hong Kong last year was 18.1 times the median annual pretax household income, the survey showed.

While that is a modest improvement in affordability compared with 19 times in the previous year, US-based Demographia considers a score of more than 5.1 as "severely unaffordable", according to its website.

Hong Kong's median multiple "represents a substantial deterioration in its housing affordability", Demographia said in the report, citing a median multiple of 11.4 times in 2010.

The dearth of affordable housing in Hong Kong has been a persistent headache for Hong Kong's chief executive Leung Chun Ying, despite a raft of taxes and mortgage caps introduced under his administration.

Prices of secondary homes, which account for about 70 per cent of volume, are up nearly 40 per cent since he took office in July 2012 and increased 7.7 per cent last year.

They are hovering just 2.6 per cent shy of their September 2015 record.

Sydney held its title as the second-costliest housing market in the world, with a median multiple of 12.2, according to the Demographia survey.

Canadian city Vancouver was the third-most expensive, while New Zealand's Auckland ranked fourth.

The following areas rounded up the top 10 least affordable housing markets: Californian city San Jose, Melbourne, Hawaii's Honolulu, Los Angeles, San Francisco and Britain's Bournemouth and Dorset.

Singapore got a 4.8 median multiple in the scoring system, which placed it in the "seriously unaffordable" band.

This is a band lower than the highest "severely unaffordable" band, for housing markets that scored 5.1 and more.

Demographia's report said that Singapore's 4.8 median multiple score was an improvement from the 5.1 median multiple in 2013, when Singapore was added to the report.

It added that Singapore "has perhaps the most land constrained geography of any major metropolitan area in the world, occupying a highly developed island, with no mainland periphery within its national jurisdiction".

This meant there is "virtually no potential for greenfield development" and that it is "difficult to maintain a competitive supply of land".

The report noted that the Housing Development Board has "materially increased the rate of construction, and the additional supply appears to have produced the expected result, better housing affordability".