China’s top legislature has said Hong Kong courts have no power to rule on the constitutionality of legislation under the city’s Basic Law, which includes a proposed ban on face masks.

Beijing insisted it held the sole authority to rule on constitutional matters in the region, and analysts say this spells disaster for Hong Kong’s rule of law – a bedrock of its success as an international financial hub.

The statement came a day after Hong Kong’s high court ruled that a ban on wearing face masks during public demonstrations that have rocked the financial hub for more than five months was unconstitutional.

“Whether the laws of the Hong Kong Special Administrative Region comply with the Basic Law of Hong Kong can only be judged and decided by the standing committee of the National People’s Congress,” said Jian Tiewei, a spokesman for the Chinese legislative affairs commission. “No other authority has the right to make judgments and decisions.”

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Jian said the ruling had “severely weakened the governance” of Hong Kong chief executive Carrie Lam and the city government.

The embattled Hong Kong chief executive, Carrie Lam, proposed a ban on face masks as the pro-democracy demonstrations escalated. Protesters had been using masks to hide their identities in public. The proposal was widely criticised by supporters of the anti-government movement who saw it as posing a risk to demonstrators.

Hong Kong’s high court ruled on Monday that colonial-era emergency laws, which were revived to justify the mask ban, were “incompatible with the Basic Law”, the mini-constitution under which Hong Kong was returned to China in 1997.

The statement from China comes amid chaos in Hong Kong where pro-democracy protests have been going for five months. Over the past 24 hours police have fought running battles with protesters trapped inside a university campus. Polytechnic University was surrounded by a security cordon on Tuesday morning. Overnight several groups of protesters were met by tear gas as they tried to escape. Police have said protesters inside have no option but to surrender.

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Analysts say China’s move has dealt a serious blow to Hong Kong’s rule of law and the “one country, two systems” policy, which has granted Hong Kong extensive autonomy since the handover from British rule and underpinned its success as an international finance centre. It has also rendered Hong Kong’s courts ineffective since it can arbitrarily overrides their decisions.

Kenneth Chan, a political science professor at the Hong Kong Baptist University, said: “Hong Kong’s judicial system is now at risk of submitting to [China’s] Marxist-Leninist ‘socialist legal system”, which demands the law and the courts serve the Communist party as instruments of power struggle.

“Beijing is doing itself and Hong Kong a disservice because it undermines the faith left in the system of Hong Kong as a global financial hub.”

Johnny Lau, a political commentator on Chinese politics, said Beijing had shown that it had “run out of patience” with the one country, two systems policy.

“Now, even the last bastion of the rule of law has been destroyed and [the statement] has made clear that the law must serve politics,” said Lau, adding that president Xi Jinping had already advocated in Hong Kong in 2008 “the collaboration of powers” instead of the “separation of powers”.

Lau pointed out that China has already shown in a key Communist Party meeting, the fourth plenum, its desire to impose more direct control over Hong Kong. “The move shows that Beijing is putting Hong Kong’s legal system under Beijing’s direct control.”