HONG KONG (Reuters) – The legal chief of Beijing’s representative office in Hong Kong said on Saturday growing calls for independence could make the territory’s current “one country, two systems” constitutional framework unsustainable.

Chinese leaders are increasingly concerned about a fledgling independence or secessionist movement in the former British colony of Hong Kong, which returned to mainland rule in 1997 amid promises of wide-ranging autonomy including judicial independence under the formula of “one country, two systems”.

The unusually strong comments by Wang Zhenmin, an official at the Central Liaison Office, China’s top representative office in Hong Kong, came ahead of the 20th anniversary of the handover of power to China.

Hong Kong will be on high alert ahead of the July 1st celebrations when President Xi Jinping is widely expected to attend the swearing in of leader elect Carrie Lam.

Speaking at a seminar in the territory, broadcast on local cable television, Wang attacked the separatist movement and said Hong Kong must act to defend China’s sovereignty.

“The more Hong Kong fails to actively defend (China’s) sovereignty, national security and development interests in accordance with the law, the more wary the country will be about Hong Kong’s high degree of autonomy and the ‘two systems’. There would be less room for its autonomy,” Wang said.

He said Beijing was also “disheartened” at the prospect separatists might enter the Hong Kong establishment or education system.

“If the two systems have been severely disrupted or even been used to damage one country, (China) will feel very unsafe…If one’s own existence has become a problem, no nation will continue the arrangements of ‘two systems’,” he said, according to footage of the same speech carried on government funded RTHK.

China has promised Hong Kong’s capitalist system would remain unchanged for 50 years, but it has not made clear what will happen in 2047. Some in Hong Kong fear Beijing may look to impose mainland rule on the territory before then.

Last year, China’s parliament intervened in a Hong Kong court case by passing a ruling on the Basic Law, as the territory’s mini-constitution is known.

It was one of Beijing’s most direct interventions into Hong Kong’s legal and political system since the 1997 handover.

Wang previously said on Friday that Hong Kong should have “respect and awe” for China’s system, to which it would have to adapt, government funded RTHK reported on Friday.

(Reporting by Michelle Price; Additional reporting by Venus Wu and Julie Zhu; Editing by Ros Russell)