In the heart of Mong Kok, one of the most densely populated districts on earth, an abandoned Hong Kong police van is enveloped in the student-led demonstrations paralyzing swathes of the city. Along with yellow ribbons and flowers, symbols of the city's pro-democracy movement, protesters have taped a hand-written placard in Chinese and English to the side of the locked and undamaged vehicle.
"We can't accept the Hong Kong police becoming the Gong An," it reads - a reference to China's feared Public Security Bureau, which enjoys virtually unfettered powers on the mainland.
The stranded police vehicle and the protesters' warning encapsulate the dilemma that the mass protests pose for China's rulers and the authorities in Hong Kong. They need to contain the campaign for democracy in one of Asia's leading financial hubs without the tools employed on the mainland to suppress dissent, including sweeping powers of arrest, indefinite detention, compliant courts and a controlled media.
While People's Liberation Army forces are stationed in Hong Kong, they have remained in their barracks. They will only be deployed on the streets if rioting and looting break out and the local police are unable to contain the violence, said two people with ties to the central government leadership.
"The mobilization of PLA troops in Hong Kong is a last resort and only if things got totally out of control," one of the people said.
As tens of thousands of protesters gather for a sixth day, their demand for the right to choose their leaders in fully democratic elections poses the biggest popular challenge to the ruling Communist Party since Chinese president Xi Jinping took power two years ago. The Umbrella Revolution, so called for the protesters' use of umbrellas to shield against pepper spray, comes at an inopportune time for Xi. He is trying to steer a slowing economy while moving against powerful vested interests in one of the most wide-ranging purges and anti-corruption campaigns since the Communists came to power in 1949.
"It is a frontal challenge to their authority," Regina Ip, a lawmaker and a top advisor to Hong Kong's embattled political leader, chief executive Leung Chun-ying, says of the protests. "People have to understand how Beijing sees this... China feels threatened," Ip told Reuters.
At the forefront of this challenge is student leader Joshua Wong Chi-fung, a skinny 17-year-old with a mop of straight black hair framing his angular face.