-- Supply is never core one among housing issues.
-- Any inflation is always an issue of currency.
-- State-owned corporate and credit system plays a role.
-- If everyone knows the price will never go down, it will certainly have nowhere to go but up.
-- The housing price will keep going up until crash.
A simple logic below explains how the bubble has been inflated by the oversupply of currency, which is a result of China's running state-owned credit system and foreign currency reserve policy.
Firstly, the housing market in China is not allowed to crash at any time by all interests. When an asset's price does not fall forever, it will certainly become a place for money to rush in and its price thus will keep being pushed up if it happens to be in an economy where there are much more money in circulation than needed.
There are huge state-owned corporates, who can access cheap credits and have no worry about loss, to speculate on lands. There are also accumulated money, derived from long term trade surplus, in private system .
There is no middle one such as being flat because it is not possible for land to be suppled faster than money is printed out to buy the earned dollars or to be put into state-owned bank system.