There are currently a host of half-finished huge buildings that are not being completed. For instance, I can see a bunch from my window. This is most likely due to lapsed demand and reduced speculative investment in the sector.
This is really just a delayed adjustment along the lines of an established national change, Shenzhen possibly encountered the slowdown later owing to increased expectations/hype/financing availability and special economic and political darling status.
I would say from physical observation that the second half of last year was the real slow down, things haven't changed much since then.
The local real estate market is pretty expensive... a lot of people who bought apartments 10 years ago are now USD multi-millionaires, despite having real incomes as low as 1-2000USD/month. As a consequence of consistent price growth, purchasing a small apartment now costs about the same as Sydney, with a median price above USD$1M. It is fairly difficult to rent a halfway decent apartment under about 6000CNY (~1000USD)/month, many pay double that or more.