The United States has condemned China's "continuing assault on democratic institutions in Hong Kong", after Beijing announced plans to change the electoral system there.
China's National People's Congress (NPC) unveiled the plans on Friday.
One proposal would require all candidates standing for Hong Kong's assembly to be approved by a committee of members loyal to Beijing.
The move follows the imposition of a tough security law last year.
Critics say Beijing is crushing dissent and removing the "one country, two systems" agreement it made with the UK.
Under the agreement, Hong Kong, a former British colony, was allowed to continue with its own legal system and have rights including free speech and freedom of the press.
Fears that that model is being eroded led to huge pro-democracy protests in 2019. Some turned violent and Beijing imposed the National Security Law, which it said would target "sedition" and bring stability.
Thousands of lawmakers have gathered for the annual NPC meeting in Beijing. The rubber-stamp parliament is expected to also discuss and approve economic growth targets and environmental policies from the central government.
How have the US and others reacted?
State department spokesman Ned Price said the move was "a direct attack on Hong Kong's autonomy, Hong Kong's freedoms and the democratic processes".
"If implemented these measures would drastically undermine Hong Kong democratic institutions," he said.
Mr Price also said Washington was working with allies at "galvanising collective action" against alleged Chinese human rights abuses of Muslim minorities in Xinjiang and "repression" in Hong Kong.
Earlier the EU called on Beijing to "carefully consider the political and economic implications on any decision to reform the electoral system of Hong Kong that would undermine fundamental freedoms, political pluralism and democratic principles".
The UK Foreign Office, meanwhile, urged China's authorities to "uphold their commitments to the people of Hong Kong, including respecting their fundamental rights and freedoms, and Hong Kong's high degree of autonomy".
Lord Chris Patten, former British governor of Hong Kong, went further, saying China's Communist Party had "taken the biggest step so far to obliterate Hong Kong's freedoms and aspirations for greater democracy under the rule of law".
What's planned for Hong Kong?
NPC vice-chairman Wang Chen told lawmakers that changes were needed as "the rioting and turbulence that occurred in Hong Kong society reveals that the existing electoral system has clear loopholes and deficiencies". He said "risks in the system" needed to be removed to ensure "patriots" were in charge.
Premier Li Keqiang warned that China would "resolutely guard against and deter" interference by external forces in Hong Kong's affairs.
The week-long NPC session will discuss the elections issue and no text has yet been made public, although Mr Wang and media sources did set out some areas to be discussed.
The city's heavily pro-Beijing electoral committee would get new powers over the parliament, or Legislative Council (LegCo).
The committee would effectively be able to vet all LegCo candidates and elect many of its members, diluting the number directly elected by the public.
Willie Lam, China analyst at the Chinese University of Hong Kong, told the AFP news agency that if the new NPC measures passed as he expected they would "effectively wipe out any remaining opposition".
How has the pro-democracy campaign been targeted?
The Basic Law, agreed with the UK before the return of sovereignty in 1997, allowed for an "ultimate aim" of universal suffrage, including the choice of leader, or chief executive.
Subsequent NPC Standing Committee rulings, however, ensured Beijing would have control over who was appointed.
Pro-democracy moves continued and came to a head with mass rallies in 2019. Last year, Beijing imposed the security law.
Scores of arrests have been made. Last week, 47 pro-democracy activists were charged with "subversion" under the new law and could face life in prison.
What is the NPC and what will it do?
The annual meeting has nearly 3,000 delegates representing provinces, autonomous regions, and the special administrative regions of Hong Kong and Macau.
While the NPC in theory is the country's most powerful institution, in reality the lawmakers usually end up approving plans and policies decided beforehand by the central government.
On Friday, Mr Li said the country had set its economic growth target at above 6%. and updated the NPC on climate control targets.
Over the next few days, the congress will also formally approve the 14th Five-Year-Plan - the economic strategy for the country.
President Xi Jinping is also likely to highlight China's achievement in "eradicating absolute poverty" - something the country announced last week.