An army-linked newspaper in China has run photos of a week-old military drill in Hong Kong, a move analysts described as a warning to Beijing’s critics as the city grapples with a wave of anti-government protests.

The People’s Liberation Army (PLA) has maintained a garrison in Hong Kong since the former British colony was returned to Beijing in 1997, but its troops generally keep a low profile and are rarely seen in uniform in public.

The unit’s routine military exercises have not attracted much attention in the past.

But a PLA-affiliated newspaper posted photos of the week-old military drill on Tuesday — a day after pro-democracy protesters ransacked Hong Kong’s legislature and left anti-Beijing messages on its walls in an unprecedented show of anger.

Huge rallies have shaken the semi-autonomous territory since last month, sparked by opposition to a bill that would allow extraditions to the Chinese mainland.

The PLA Daily said on its verified account on the Twitter-like Weibo platform that the joint exercise last Wednesday — which involved ground forces, the navy and the air force — were aimed at “reviewing and raising the units’ combat abilities in emergency dispatches”.

The photos showed Chinese soldiers pointing automatic rifles on a boat, a PLA helicopter, and warships.

“The intention of this exercise is obvious. It is to warn the Hong Kong independence elements and to deter foreign interference in Hong Kong affairs,” said Ni Lexiong of the Shanghai National Defence Strategy Institute.

“If things develop to a more extreme level, and if the Hong Kong government isn’t able to cope with the situation, the central government may use troops.”

‘Blatant challenge’

Zhu Yonghua, a naval commander involved in the exercise, told the Communist Party mouthpiece People’s Daily that the drills will help improve the Chinese military’s ability to “help the Hong Kong government protect the lives and property of its citizens”.

Beijing on Tuesday called for a criminal investigation into the storming of the Hong Kong legislature, which it described as a “blatant challenge” to the “one country, two systems” policy that has given the city its semi-autonomous status for 22 years.

China has also lashed out against “foreign interference” in Hong Kong.

“The announcement of the PLA exercise by China’s state media is a not-so-subtle message to Hong Kong and the world that China would ultimately be willing to resort to force in order to secure its interests in Hong Kong,” said Adam Ni, a researcher on Chinese foreign and security policy at Macquarie University in Australia.

The Chinese military received official ownership of a piece of prime Hong Kong waterfront land Saturday, which will allow its warships to berth in the city’s famed Victoria Harbour in future.