A 2015 stats  say that locals account for 11,471 transactions; mainlanders 1,299; foreigners 581. Without verifying this data further and just for the sake of theoretical problem solving, 1,880 transactions going to non-locals is 14% of the total transactions.  When working families are squeezed so bad like they are now, 1,880 or 14% seem to be quite a big dent on the housing market dynamics (directly or indirectly).