In a high-walled Art Deco villa in the Hong Kong suburbs of Kowloon, the Vatican operates an unofficial diplomatic mission, its only political outpost of any kind in China.

The mission keeps such a low profile that it isn't listed in the Roman Catholic Church's formal directory of every priest and property in the city. The two monsignors who staff the outpost have no formal standing with Beijing or the Hong Kong government, and they don't conduct official work, not even meeting Hong Kong officials. The tenuous foothold is a sign of the delicate position in China of the world's largest Christian denomination, many of whose members in Hong Kong staunchly support the city's democracy movement.

And now the mission — and the Church as a whole in Hong Kong — is coming under mounting pressure as Beijing moves to extinguish opposition voices in the city under a new national security law.