HONG KONG — Hundreds of thousands of people filled the sweltering streets of Hong Kong on Sunday in an immense protest against a government plan to allow extraditions to mainland China that culminated after midnight in clashes with the police.
The mass demonstration was one of the largest in the city’s history and a stunning display of rising fear and anger over the erosion of the civil liberties that have long set this former British colony apart from the rest of the country. Organizers said they counted more than one million on the streets, or nearly one in seven Hong Kong residents.
The protest recalled the pro-democracy Umbrella Movement five years ago, which paralyzed several of the city’s main commercial districts but failed to persuade the government to make any concessions. Since then, China’s ruling Communist Party has been gradually exerting more influence over Hong Kong.
The local authorities have rejected demands for free elections and ousted opposition lawmakers, and critics say Beijing’s supporters are chipping away at the independence of the territory’s courts and news media.
The pressure on Hong Kong reflects a broader tightening of controls across China under President Xi Jinping, the party’s general secretary.
The crowd of protesters, which stretched more than a mile, represented a dramatic rebuke of the Communist leadership and a potential political crisis for Beijing and Carrie Lam, the leader it selected to govern Hong Kong.
“I think this law will take away our freedoms if it is implemented,” said Peter Lam, a 16-year-old high school student, referring to the extradition law that Ms. Lam is trying to push through with Beijing’s support. “We will not have the right to express ourselves. So we must stand up and express ourselves today.”
The police estimated there were 240,000 protesters at the peak of the demonstration, but organizers said it was the biggest rally since more than one million residents gathered in 1989 in support of the student-led democracy movement that was crushed in Tiananmen Square.
The crowd that poured through the canyons of downtown skyscrapers was so vast that many people said they had been stuck in subway stations waiting to join the protest, and some trains skipped stations because of overcrowding.
The immediate focus of the protest was a proposal to allow extradition to mainland China, which critics are worried the authorities will use to send dissidents, activists and others in Hong Kong, including foreign visitors, to face trial in mainland courts, which are controlled by the party.
Despite the large numbers, neither Beijing nor the Hong Kong government showed any willingness to back down, and officials confirmed that a second legislative reading of the bill would proceed as scheduled on Wednesday.
But the turnout also exposed the depth of frustration with Beijing’s growing encroachment on the autonomy it promised Hong Kong when it resumed sovereignty over the territory in 1997.
In recent years, mainland Chinese police officers have been allowed to operate in a section of a new train station linking Hong Kong to China’s high-speed-rail network. A draft law that punishes disrespect for the Chinese national anthem has raised concerns about free speech in a place where soccer fans have been known to boo when the song is played. And many bookstores have stopped selling publications critical of the leadership in Beijing.
For most of the day, Sunday’s demonstration was peaceful. But tempers began to flare in the evening near the offices of the central government as the protesters, whose march had slowed to a standstill on some streets, urged the police to free up more lanes.
About 1 a.m., long after most protesters had left, riot police with helmets and shields moved in to remove a few hundred who were trying to occupy an area in front of the legislature. Some protesters pushed metal barriers and tossed bottles and sticks at the police, shouting, “Communist dogs!”
The police charged, firing pepper spray, striking people with batons and pushing the protesters away from the government complex.
Some demonstrators then temporarily blocked part of Gloucester Road, a major thoroughfare that was occupied during the Umbrella Movement. The clashes continued into early Monday morning, with both protesters and police injured.
Despite the size of the protests, the government was unlikely to be swayed, said Ivan Choy, a senior lecturer in the department of government and public administration at the Chinese University of Hong Kong.
“The major problem is that Xi Jinping holds power in China, and he is a strongman,” Mr. Choy said, referring to China’s top leader. “He will back up Carrie Lam’s decision to push forward.”
“Most people know this reality,” he continued, “but they have come out to show the world that this legislation is not the will of the Hong Kong public.”
The protesters had set off from Victoria Park in the afternoon, with temperatures in the mid-80s and scattered rains providing little relief from the humidity. Many wore white as a symbol of justice and also mourning in Chinese culture, and held signs saying, “No China Extradition” and “No Evil Law.”
They directed much of their ire toward Ms. Lam, shouting slogans for her to resign and booing as they passed a large screen displaying footage of her at a news conference.
At public events elsewhere in the city, Ms. Lam declined to answer questions about the protests. But the huge public outcry puts her in a difficult spot ahead of a vote on the bill expected later this month.
Late Sunday, the government, responding to the protests, said the bill would prevent Hong Kong from becoming a haven for fugitives. While pledging to “continue to engage, listen and allay concerns,” the statement indicated the government was pushing ahead with the bill.
The proposed legislation would allow suspects in some criminal cases to be turned over to jurisdictions with which Hong Kong has no formal extradition agreement. The immediate goal is to enable the government to send a Hong Kong man to Taiwan, where he is accused of having killed his girlfriend.
But the legislation would also allow extraditions to mainland China for the first time, with few avenues for appeal.
The legislation excludes political crimes, and the Hong Kong government has promised to monitor cases for human rights concerns. But many fear that the Chinese authorities could use charges such as bribery to target people who have angered mainland officials.
The Communist Party had promised a “high degree of autonomy” before Britain returned the territory to Chinese sovereignty in 1997, but many feel that the city’s freedoms are steadily being worn down under Beijing’s rule.
Hong Kong’s courts are far more transparent and independent than those in the mainland. Worries about Beijing’s reach have been made worse by the disappearance of people from Hong Kong into mainland custody, including a Chinese billionaire and men associated with a company that published books unflattering to mainland political leaders.
“Their judicial system is not good,” George Wan, 31, a freelance tour guide and writer at the protest, said of mainland China. He said the Hong Kong government was rushing the legislation through without properly consulting the public.
“We want to use our footsteps to tell the government we want more time,” Mr. Wan said as he waved a folding fan painted with characters that read “Oppose sending to China.”
Young people and families were prominent in the crowd, with parents bouncing toddlers on their hips and leading young children by the hand. One child clutched a sign saying, “Protect my future.”
[Read: The outcry over the extradition proposal is Hong Kong’s biggest in years.]
The protest also drew people who normally stay on the sidelines. Lee Kin-long, 46, said he and his wife felt they needed to attend.
“This law is dangerous, and not just for activists,” he said. “We are not activists. Even as regular citizens, we can’t stand to see China eroding away our freedom.”
Opposition to the legislation has been building for weeks, including a scuffle among lawmakers and an April demonstration that was the city’s biggest in five years.
Worries about the proposal have inspired hundreds of petitions from student and alumni associations, religious organizations and trade groups. Business associations have expressed fear that the measure would harm Hong Kong’s reputation as a commercial center. Press freedom groups have objected too, citing the frequent jailing of journalists in the Chinese mainland.
Foreign governments including the United States, Britain and Canada have also expressed concerns.
In Washington, the State Department noted that it had documented “rights violations and abuses carried out by China’s legal system, as well as general deterioration of respect for the rule of law.”
“Continued erosion of the ‘One country, two systems’ frameworks puts at risk Hong Kong’s established special status in international affairs,” the department said in a statement.
An official Chinese newspaper, the China Daily, defended the extradition measure in an editorial and accused “foreign forces are seizing the opportunity to advance their own strategy to hurt China by trying to create havoc in Hong Kong.”
Lawyers in Hong Kong responded to the legislation on Thursday by dressing in black for a silent protest march. A high court judge who signed a petition organized by University of Hong Kong alumni was reprimanded by the city’s chief justice.
The last time residents of Hong Kong turned out in such large numbers over a single issue was in 2003, when half a million marchers expressed their opposition to proposed national security legislation prohibiting sedition, subversion and treason against the Chinese government.
That legislation, known as Article 23, was shelved after so many people mobilized against it, arguing that it threatened civil liberties enshrined in Hong Kong’s version of a constitution. Polling by the University of Hong Kong has indicated that opposition to the extradition plan is even higher.
But pro-democracy lawmakers have said that unless the government backs down, the measure is likely to pass in the local legislature, where pro-Beijing lawmakers hold 43 of 70 seats. Only half the seats are elected by popular vote.