Beijing must intervene in a Hong Kong political dispute to deter advocates of independence for the city, China's top legislative panel said, calling their actions a threat to national security.

The Standing Committee of China's rubber-stamp legislature, the National People's Congress, said in a statement that Beijing could not afford to do nothing in the face of challenges in Hong Kong to China's authority, China's official Xinhua News Agency reported late Saturday.

On Sunday, thousands of people marched in Hong Kong to voice their opposition against China's plan to intervene in a political dispute, saying the move would undermine the territory's considerable autonomy and independent judiciary.

The dispute in Hong Kong centers on a provocative display of anti-China sentiment by two pro-independence lawmakers, Sixtus Leung and Yau Wai-ching, at their swearing-in ceremony last month.

The legislative panel in Beijing said the two Hong Kong lawmakers' words and actions "posed a grave threat to national sovereignty and security," Xinhua reported.

If such a situation were to persist, the committee said, it would hurt the interests of Hong Kong's residents and the country's progress. "The central government cannot sit idly and do nothing," it said.

The statement followed discussions by the top legislative panel on issuing an interpretation of an article in Hong Kong's constitution, known as the Basic Law, that covers oaths taken by lawmakers.

Leung and Yau, who are from the radical Youngspiration party, altered their oaths to insert a disparaging Japanese term for China. Displaying a flag reading "Hong Kong is not China," they vowed to defend the "Hong Kong nation." Leung crossed his fingers while Yau used the F-word in her pledge.

Their oaths were ruled invalid, but attempts at a do-over have resulted in mayhem in the legislature's weekly sessions.

Saturday's comments indicated that the panel intended to use its interpretation of the article to send a strong message against separatism — and could ultimately lead to the democratically elected lawmakers' disqualification from office.

Such an outcome would be favorable to China's Communist leaders, who are alarmed by the former British colony's burgeoning independence movement, but is also likely to plunge their troubled relationship into fresh turmoil.

Maria Tam, a Hong Kong deputy to the National People's Congress, told reporters in Beijing on Saturday that the legislative panel has the "final say" on the dispute and that Hong Kong's highest court would accept the panel's interpretation as binding.

Demonstrators in Hong Kong, meanwhile, held signs Sunday saying "Defend the rule of law" and calling for the city's Beijing-backed chief executive Leung Chun-ying to step down.

Some said that if China's top legislative panel issued its own interpretation on oath-taking, it would effectively undermine a Hong Kong court's ongoing review of the case.

"In (the) long run, that will damage our confidence in the court," said Alvin Yeung, a legislator. "That will, in the long run, damage the international investors' (confidence) in Hong

Kong's stability and the rule of law and of course how our court functions."