Hong Kong has some of the most unaffordable housing

It has the highest price-income ratio.

According to Bloomberg, for all the talk of how expensive it is to buy a house in London or New York, the most expensive major cities in the world are all in Asia. In Hong Kong, Mumbai, Beijing and Shanghai, it now takes more than 30 years for a household with the local median income to buy a 90 square meter (970 square foot) apartment. That's according to Oxford Economics examination of price-to-income ratios across the world.

And the return from rents in Mumbai, Shanghai, Beijing, and also Delhi are "remarkably low," which could be an indicator that the valuations in those cities are "stretched." In all four cities, gross rental yield was lower than 10 year government bond yields in 2016, unlike places such as Tokyo, Sydney, New York and Seoul. "We expect housing price increases to moderate in the coming years across Asia, with outright falls possible in some markets," economists Tianjie He and Louis Kuijs wrote in the report. In addition to rising supply and efforts in some places to cool red-hot markets, changes in interest rates will also put downward pressure on prices.

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