BEIJING--China’s Hong Kong affairs office warned on Wednesday that the city will never be calm unless “black-clad violent protesters” were all removed, describing them as a “political virus” that seeks independence from Beijing.

The strongly worded statement comes amid mounting concerns among democracy activists that China is tightening its grip over the former British colony, while a lockdown to prevent coronavirus infections has largely kept their movement off the streets.

The Hong Kong and Macau Affairs office warned that China’s central government will not sit idly by “with this recklessly demented force in place” and that China’s central government has the greatest responsibility in maintaining order and safeguarding national security.

“The scorched-earth action of the black-clad violent protesters is a political virus in Hong Kong society and a big enemy to ‘one-country-two-systems,’” the office said in a statement on Wednesday.

“As long as the protesters are not removed, Hong Kong will never be calm,” it said.

The Asian financial hub was rocked in 2019 by months of massive, and sometimes violent, political protests over a now-withdrawn extradition bill that would have allowed people to be sent to mainland China for trial.

Many young protesters dressed in black fought running battles with Hong Kong police as the demonstrations evolved into calls for greater democracy.

Protesters said Beijing was seeking to erode the “one country, two systems” style of governance that guarantees broad freedoms for Hong Kong since its return to Chinese rule in 1997.

Beijing rejects criticism that it is seeking to encroach on the city’s much-cherished freedoms.

Hong Kong riot police dispersed a crowd of 300 pro-democracy activists, some wearing black, late last month--the first sizable protest since the government imposed a ban on public meetings at the end of March to curb coronavirus infections.

The arrests of 15 activists in April, including veteran politicians, a publishing tycoon and senior barristers, thrust the protest movement back into the spotlight and drew condemnation from Washington and international rights groups.

Beijing’s top representative office in Hong Kong on Saturday condemned what it described as extreme radicals for holding illegal assemblies over the Labor Day holiday and accused them of undermining the rule of law.

A war of words has intensified in the past few weeks, with Beijing’s top official in Hong Kong urging the local government to work to enact national security legislation “as soon as possible”, fueling worries over what many see as encroachment on the territory’s freedoms.

Fear that Beijing is flexing its muscle over Hong Kong risks a revival of anti-government protests after months of relative calm amid social distancing rules to curb the spread of the coronavirus.

Hong Kong’s economy recorded in the first quarter its deepest annual contraction since at least 1974, as the coronavirus pandemic dealt a heavy blow to business activity, already in decline following the anti-government protests.

The Hong Kong and Macau Affairs office said that while there were many factors contributing to Hong Kong’s economic woes, the main problem was anti-government protests.

“Hong Kong’s biggest trouble comes from within, that is the violent forces openly calling for and engaging in ‘lanchao,’” said the office, referring to a scorched-earth tactic.