China has doubled the number of troops in Hong Kong as pro-democracy protests there escalated over the weekend.

About 12,000 Chinese troops are now stationed in Hong Kong, according to reports. The semi-independent territory’s citizens have protested all summer, sometimes engaging in violent clashes with police, against what they say is stifling authoritarianism from China.

Over a dozen people have been injured and over 150 arrested, during the 17th consecutive weekend of protests, police said.

The demonstrations were originally sparked by outrage over an extradition law that Hong Kong residents say would allow Chinese authorities to effectively “kidnap” them on little evidence and force them to face the court process in mainland China. The concern over the law soon ballooned into fear that China plans to throw out its “One Country, Two Systems” policy regarding Hong Kong.

Last month, about 5,000 protesters swarmed Hong Kong International Airport, causing the major travel hub to shut down and cancel all flights.

The latest protests over the weekend were peaceful at first and meant to celebrate five years of the pro-democracy Umbrella Movement, but they quickly turned ugly, protesters starting street fires and throwing bricks on government buildings and petrol bombs while police responded with force. Protesters sang their anthem, “Glory to Hong Kong,” and chanted “Fight for Freedom; Liberate Hong Kong” during the demonstrations.

Police said they used a warning shot of live ammunition against protesters in Wan Chai after police were “surrounded and attacked by a large group of violent protesters.” Police also shot tear gas and a water cannon filled with blue dye at demonstrators, which is meant to make them easier to spot later.

The weekend’s particularly violent spate of protests come just before the mainland celebrates the 70th anniversary of the People’s Republic of China on Tuesday.

China previously vowed a severe response to the demonstrations, saying protesters were engaging in “terrorist activities.”