Thousands of Chinese riot police staged a drill just across the border from Hong Kong, in what appeared to be a thinly veiled warning from Beijing about its ability to end two months of protests in the global financial hub.

The exercise, which took place Tuesday in Shenzhen, a city in southern China that borders the semi-autonomous city, instantly attracted online attention given the close resemblance between the drill and the ongoing clashes in adjacent Hong Kong. The footage showed squads of police facing down "protesters" dressed in construction hats and facemasks, reminiscent of demonstrators in Hong Kong.

The head of Beijing's Cabinet office responsible for Hong Kong says the territory is facing its "most severe situation" since the handover from British rule in 1997. Zhang Xiaoming was speaking to Hong Kong residents attending a seminar yesterday in the mainland city of Shenzhen. He said the central government was "highly concerned" about the two months of daily street protests against the administration of Chief Executive Carrie Lam and considering further measures to take. Hong Kong was returned to China under the framework of "one country, two systems," which promised the city political, civil and economic freedoms not allowed under Communist Party rule on the mainland.