Over the past few weeks, relations between Hongkongers and mainlanders have suddenly gone sour. First, there was the protest provoked by the Dolce & Gabbana outlet in Tsim Sha Tsui stopping a Hongkonger from taking photos of the shop, but not mainland tourists.
Then, the row was fuelled by a Beijing professor's rude comments - amid a war of words between angry netizens on both sides over a mainlander eating on the MTR - that some Hong Kong people were dogs.
These may well be isolated incidents, but deep below these boiling public sentiments is a sense of threat that mainlanders are overwhelming Hong Kong, buying up local properties and infant formula. Pregnant mainland women have flooded local hospitals, inducing angry local women to take to the street to demand government action to stop them.
As I wrote in this column a year ago, as the city integrates further with the mainland and becomes a national market, pain will come with the economic gain. The purchasing power of even a tiny percentage of the mainland will be able to shape, overwhelm or even distort the local economy; the scale of such change needs to be fully factored in to policy planning, and it calls for a rethink of the 'two systems' relationship.
The clash is not merely economic or even cultural. The brewing tensions have arisen out of the original 'two systems' design not being able to cope with the new social and economic realities emerging over the past decade as mainland China rises to become the second-largest economy in the world, breeding the new rich and middle classes in growing numbers in the big cities.
The legal identity of Hongkongers has been built on the Basic Law definition of permanent resident entitled to a passport separate from the national one, as if it had a 'subnational' status.