Hong Kong police have fired pepper spray at a rally outside the office of a Chinese representative to protest the central government attempts to curb a fledgling independence movement.
Minor scuffles broke out as some protesters hurled bottles at police. At least one protester was arrested and around 20 were hit with pepper spray.
A ruling on Monday from a top committee of China's parliament, the National People's Congress, is expected to effectively bar the recently elected lawmakers Yau Wai-ching, 25, and Baggio Leung, 30, from taking office.
The pair set off a fierce debate when they pledged allegiance to the "Hong Kong nation" and displayed a "Hong Kong is not China" banner during a swearing-in ceremony for the city's legislative council in October. Their oaths were not accepted and their right to re-take them is being challenged in the local courts by the Hong Kong government.
The congress's standing committee is not waiting for the judgment, however. It has discussed invoking its rarely used power to interpret Hong Kong's mini constitution, the Basic Law, to stop them taking office.
Lawmakers quoted on Chinese state television, CCTV, over the weekend described the pair as a threat to China's sovereignty and security.
The situation is seen among many across Hong Kong's legal and political elites as one of the biggest tests the global financial hub has faced since its handover to China, with some fearing its vaunted rule of law is under threat.
Britain returned Hong Kong to Chinese control in 1997 under a "one country, two systems" formula that gave the territory wide-ranging autonomy, including judicial freedom, under the Basic Law.
Earlier, thousands of protesters marched from Wan Chai to the city's Central financial district, with several hundred pressing to Beijing's Liaison Office. Organisers put the numbers at 11,000; police said 8000 turned out.