China on Thursday demanded the United States stop advancing a Hong Kong-related bill and its interference in Hong Kong affairs on Thursday, after US lawmakers held a news conference to back the bill.

US House of Representatives Speaker Nancy Pelosi and a bipartisan group of members of Congress held the media event on the "Hong Kong Human Rights and Democracy Act of 2019". Hong Kong separatists, including Joshua Wong Chifung and Denise Ho Wan-see, attended the event.

China is strongly dissatisfied and firmly opposed to the move, Foreign Ministry spokesman Geng Shuang said on Thursday.

Pelosi and other US politicians "failed to distinguish right from wrong" despite China repeatedly expressing its solemn stance over US meddling in Hong Kong affairs, Geng said.

They were "brutally interfering in China's internal affairs" by threatening to advance the bill, contacting Hong Kong separatists and making irresponsible remarks over Hong Kong affairs, Geng added. He reiterated that no foreign forces are allowed to interfere in Hong Kong affairs, which belong purely to China's internal affairs.

"We strongly urge the US to... stop its interference of any kind in Hong Kong affairs, stop advancing the bill, stop endorsing Hong Kong's violent and radical forces and separatists, and stop abetting words and deeds that harm the prosperity of the special administrative region," Geng said.

The Office of the Commissioner of the Foreign Ministry in Hong Kong also slammed the US politicians' move, which is at odds with their "claimed support for 'one country, two systems'" and has "fully exposed their hidden political agenda".

The office said in a statement that anyone without bias will acknowledge that the people of Hong Kong are enjoying unprecedented democracy, rights and freedom under the law.

The statement also emphasized no one has the right or freedom to carry out separatist activities or a "color revolution" in Hong Kong, nor are they allowed to act above the law or disrupt the rule of law and public order.

"Stopping violence, ending the chaos and restoring order represent the freedom and justice that the overwhelming majority of people in Hong Kong truly aspire to," the statement said, urging the US politicians to "follow the mainstream public opinion in Hong Kong".

Reintroduced in the US House of Representatives in June, the act calls for an annual assessment of Hong Kong's autonomy before extending the US' special treatment to the city, among other measures.