As a way of reviving Hong Kong's battered economy after the 2003 outbreak of severe acute respiratory syndrome, the Individual Visit Scheme was an almost immediate cure. It filled empty hotels, and restaurant owners and retailers rejoiced at the reappearance of travellers on the city's once-deserted streets.
Over the nine years since, the scope of the scheme - which allows mainland tourists to travel to Hong Kong by themselves rather than in a tour group - has been expanded from the initial four cities to 49, making 270 million people eligible to visit Hong Kong.
The impact has been remarkable, with the Tourism Board reporting that 3.1 million visitors flooded in in January, up 23.9 per cent on the same period last year. They accounted for about three quarters of that month's total of 4.14 million visitors.
In 2002 Hong Kong received 16.6 million visitors, of whom 6.9 million, or 41.6 per cent, were from the mainland. By last year the number had soared to 41.9 million, 67 per cent of whom came from the mainland.
But not everyone is happy with the fallout from the influx.
Bookshops have been replaced by outlets selling jewellery, watches and electronic appliances to the big spenders. Local mothers have difficulty buying milk formula - a sought-after commodity for mainlanders - and consumers confronted with rising inflation blame the tourists for soaring prices.
When the mainland's simplified characters finally made it on to outdoor advertisements and restaurant menus, alongside the traditional ones preferred in Hong Kong, the anger intensified.