Tens of thousands of Hong Kong residents have taken to the streets to demand their government halt a plan that would make it easier to extradite people to the secretive judicial system in mainland China.

The march organisers estimated that more than 100,000 people filed through central Hong Kong on Sunday. Police said the march drew 22,800 people at its peak.

The plan proposed by the city’s security bureau, and pushed by Carrie Lam, the chief executive, would allow Hong Kong to send criminal suspects requested by China, Taiwan or Macau. None of those jurisdictions has a rendition agreement with Hong Kong. Hong Kongers fear the law will allow China to demand that Hong Kong turn over political dissidents, religious workers and business people whose work may violate some yet-to-be-written law.

“They say if you’re innocent you shouldn’t be afraid,” said Alex Ho, a Catholic school teacher who marched most of the route carrying his 18-month-old daughter, Stella. “But the legal system in China changes. They can make up the law and say that people did whatever they want.”

It was the biggest protest for several years, activists and journalists said, in a city known for a 79-day occupation for democratic elections in 2014.

Some protesters said they showed up to support nine activists who were convicted earlier this month of public nuisance charges related to the 2014 event. Four of those were sentenced to prison, with two professors getting 16-month terms. Their supporters collected thousands of dollars for their appeals.

Fears that the amendment will pass led one prominent resident to flee. Lam Wing-kee, who smuggled gossipy books about Chinese leaders, landed in Taiwan last week where he plans to seek residency. Lam disappeared in 2015 and resurfaced months later to say he’d been kidnapped and held by Chinese security. “If the ordinance is passed, I won’t be allowed to leave, because I have been charged with a crime and am wanted for it,” he told Bloomberg before leaving.

Ronny Tong Ka-wah, a member of the executive council, the city’s advisory unit, urged the government not to favour public pressure. “If the government surrenders just because there are some opposing voices, I am afraid it will be difficult to have effective governance in the future,” he said, according to the South China Morning Post.

The protest drew people who said they have never marched, or have not done so in years. “Everyone, whatever their background, everyone will be caught up by the central government [in Beijing] without reason,” said a civil servant who would identify herself only as Ada. She said she had not protested since 1989 when students sought democracy in China.

Think about the booksellers and their forced confessions, said her friend, Iris. “You’re an idiot if you believe Carrie Lam,” she said.

Hong Kong has many extradition agreements, but not with China, Taiwan or Macau in the nearly 22 years since Britain relinquished the territory. Hong Kong crafted this new proposal after Taiwanese officials asked Hong Kong to send a 19-year-old man wanted for the murder of his pregnant girlfriend. Hong Kong authorities arrested Chan Tong-kai but could only charge him with money laundering.

Lam has urged Hong Kong’s legislature to pass the amendment before July. Otherwise, the city’s courts might free the suspect. Lawmaker Alvin Yeung offered a counter-proposal on Friday that would allow Hong Kong’s courts to try Chan for murder in local courts.

Many international organisations have asked Lam to alter the proposal. That includes Hong Kong’s most influential business group, the American Chamber of Commerce, which said it could sweep business people into China’s legal orbit. Taipei officials say they will not sign any agreement that implies Taiwan is part of China.

Margaret Ng, a former lawmaker, addressed the crowd at the end of the route. “People from all the world must support Hong Kong,” she said once off the stage. “It’s the freest city in China … If they pass it, it will be very difficult to see Hong Kong as a different place from China.”