Hong Kong's border with mainland China is a de facto international boundary under the "One Country, Two Systems" model, which lets the city maintain its own liberties and free market economy. The Hong Kong side -- tens of kilometres from the city's downtown -- is predominantly rural while the Chinese side is dominated by the urban sprawl of Shenzhen.

Hong Kong begins enforcing a mandatory two-week quarantine for anyone arriving from mainland China, a dramatic escalation of its bid to stop the deadly new coronavirus from spreading.