Hundreds of thousands of people have marched in Hong Kong against a law critics fear could let China target political opponents in the territory.
The controversial extradition bill would allow suspected criminals to be sent to mainland China for trial.
The changes will allow for extradition requests from authorities in mainland China, Taiwan and Macau for suspects accused of criminal wrongdoings, such as murder and rape.
The requests will then be decided on a case-by-case basis.
The protests were the biggest since the 2014 Umbrella Movement.
The government says the bill has built-in protections and will plug loopholes.
Hong Kong's leader Carrie Lam has pushed for the amendments to be passed before July. Supporters say safeguards are in place to prevent anyone facing religious or political persecution from being extradited to mainland China.
The bill's critics say those in the former British colony would be exposed to China's deeply flawed justice system, and it would lead to further erosion of the city's judicial independence.
Protesters dressed in white, marching in the sweltering heat, and included a wide range of people: business people, lawyers, students, pro-democracy figures and religious groups.
"This the end game for Hong Kong, it is a matter of life or death. That's why I come," Rocky Chang, a 59-year-old professor, told Reuters. "This is an evil law."
Hong Kong officials have said Hong Kong courts will have the final say over whether to grant such extradition requests, and suspects accused of political and religious crimes will not be extradited.
The government has sought to reassure the public with some concessions, including promising to only hand over fugitives for offences carrying maximum sentences of at least seven years.
There has been a lot of public opposition, and critics say people would be subject to arbitrary detention, unfair trial and torture under China's judicial system.
The latest proposal has come after a 19-year-old Hong Kong man allegedly murdered his 20-year-old pregnant girlfriend while holidaying in Taiwan together in February last year. The man fled Taiwan and returned to Hong Kong last year.
Taiwanese officials have sought help from Hong Kong authorities to extradite the man, but Hong Kong officials say they cannot comply because of a lack of extradition agreement with Taiwan.
The Taiwanese government has however said it would not seek to extradite the man under the proposed changes, and urged Hong Kong to handle the case separately.