Hong Kong - China's military deployed fresh troops to Hong Kong on Thursday in what it called a routine rotation. But the move came amid speculation that Beijing might try to quash the semi-autonomous city's pro-democracy protests with greater force.

As CBS News correspondent Ramy Inocencio reports, Hong Kong has been rocked by protests, violence and chaos since June 9. What started as public opposition to a proposed change in extradition rules exploded into anger and calls for the resignation of the city's chief executive. Protesters have demanded an investigation into police brutality and advocated for greater democratic reforms. The unrest has raised questions about whether China might deploy the People's Liberation Army or the People's Armed Police, a paramilitary force, in the heart of the city to silence the dissent.

The protests, which have been marred by violence, took a peaceful turn over the weekend as more than 1.5 million took to the streets to form a human chain in defiance of Beijing and the Hong Kong administration it backs.

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Another massive rally planned for this weekend, which would have seen demonstrators march to the government liaison office, was banned on Thursday by the Hong Kong police - the first time the police have taken such a measure.

The protesters have appealed the decision.

Military vehicles of the Chinese People's Liberation Army (PLA) pass Huanggang Port for a routine troop rotation in Hong Kong, August 29, 2019. XINHUA/REUTERS

Video broadcast on China Central Television showed a long convoy of armored personnel carriers and trucks crossing the border over Wednesday night, and troops in formation disembarking from a ship. Earlier, scores of soldiers ran in unison onto trucks, which the state broadcaster said were bound for ports and entry points into Hong Kong.

"This time the task has a glorious mission. The responsibility is great. The job is difficult," an unnamed major said to troops before they departed. "The time for a true test has arrived!"

The official Xinhua News Agency said it was the 22nd rotation of the People's Liberation Army's garrison in Hong Kong. The previous one was in August 2018.

The Hong Kong garrison earlier published a promotional video with scenes of soldiers facing off with people dressed like protesters.

Chinese Defense Ministry spokesman Ren Guoqiang told reporters in Beijing on Thursday that the demonstrators must abide by Hong Kong's laws.

A leader of 2014 pro-democracy protests in Hong Kong said the city's government is using the same tactics as five years ago.

"The government is just trying to threaten people with emergency law, with the entrance of the People's Liberation Army," Yvonne Leung said at a news conference.

A former British colony, Hong Kong was returned to China in 1997 under a "one country, two systems" framework, which promises the city certain democratic rights that are not afforded to the mainland. In recent years, however, some Hong Kong residents have accused Beijing of steadily eroding their freedoms.

The newly arrived Chinese troops have been educated on Hong Kong's laws and vowed to defend the nation's sovereignty, Xinhua said.

"We will firmly implement the guideline of 'one country, two systems' and the Basic Law and the Garrison Law of Hong Kong," Liu Zhaohui, the garrison's deputy chief of staff, said on CCTV.

The Garrison Law allows the Hong Kong-stationed troops to help maintain public order at the request of the city government. That has never happened, and Hong Kong authorities have said they can handle the situation themselves.

Troops stationed in Macao, another special administrative region, also completed a rotation Thursday.

The Xinhua report on the previous rotation in August 2018 did not mention "one country, two systems" or national sovereignty.