HONG KONG (AP) — Hong Kong riot police fired multiple rounds of tear gas and used a water cannon Saturday to break up a rally by thousands of masked protesters demanding meaningful autonomy after Beijing indicated it could tighten its grip on the Chinese territory.

Streets in the upscale Causeway Bay shopping area were clouded with tear gas, prompting protesters to flee as riot police marched down the road. A water cannon truck was also deployed. Police earlier issued warnings to protesters who occupied the area that they were attending an unauthorized rally and violating a government ban on face masks.

Tear gas was also fired to disperse a huge crowd in nearby Victoria Park after protesters unearthed a goal post from a soccer field and metal railings to block the park’s entrance. Several protesters were detained.

Hardcore protesters in full gear quickly regrouped in the vicinity, using plastic cones and metal railings to set up road barriers to prepare for possible further clashes with police.

The anti-government protests began in early June over a now-shelved plan to allow extraditions to mainland China but have since swelled into a movement seeking other demands, including direct elections for Hong Kong’s leaders.

A move last month by Hong Kong’s leader, Carrie Lam, to invoke emergency powers to impose a face mask ban was seen as a further infringement on freedoms guaranteed under the “one country, two systems” framework put in place when Britain returned the city to China in 1997.

Saturday’s protests marked the 22nd straight weekend of increasingly violent unrest that has hurt the reputation of one of the world’s top financial hubs. The city has slipped into recession for the first time in a decade as it grapples with the turmoil and the impact from the U.S.-China trade war.

More than 3,000 people have been detained in the protests. The civil disobedience has posed a big challenge to Beijing, which vowed Friday to prevent foreign powers from sowing acts of “separatism, subversion, infiltration and sabotage” in Hong Kong.

In a Communist Party document released after its Central Committee meeting this past week, Beijing said it would “establish and strengthen a legal system and enforcement mechanism” to safeguard national security in Hong Kong.

Hong Kong, which has a separate legal system from mainland China, has tried to enact anti-subversion legislation before, only to have the measure shelved amid formidable public opposition. Beijing may be indicating it is preparing to take matters into its own hands by having the National People’s Congress issue a legal interpretation forcing the enactment of such legislation.