Protesters numbering more than 200,000 marched through Hong Kong on Sunday in a mass rally calling for the withdrawal of a local government proposal to allow fugitives to be handed over to authorities in China, marking one of the biggest demonstrations in the city in years.

Hong Kong, an important global trade and finance hub of about 7.4 million people, has for nearly 22 years been a semi-autonomous region of the People's Republic of China with its own legal system, a legacy of its time as a British colony.

Opposition to legal amendments under debate to allow extraditions for certain crimes to jurisdictions with which Hong Kong has no such agreement — including the Chinese mainland — has been increasing for weeks, with an array of groups, including local lawmakers, legal and business organizations and even foreign governments expressing concern.

Shouting "oppose extradition to China," huge crowds of demonstrators marched peacefully along a main thoroughfare in sweltering humidity. Many held up signs or carried large banners expressing the same sentiment.

Organizer Civil Human Rights Front claimed that one million people joined the rally, though police estimated a peak figure of 240,000. That number was far larger than the previous large-scale rally on the issue on April 28 which police said at the time drew about 22,800 people, yet short of the half million that reportedly took part in a protest in 2003 over a proposed security law.

The government appeared unbowed, releasing a statement late Sunday recognizing the "large" size of the march though vowing to press ahead.

"As a free, open and pluralistic society, we acknowledge and respect that people have different views on a wide range of issues," it said, calling on the Legislative Council, the local assembly, to examine the bill "in a calm, reasonable and respectful manner to help ensure Hong Kong remains a safe city for residents and business."

Local television news showed footage of police struggling to control crowds. A police spokeswoman said that a total of seven men were arrested for alleged offenses including assaulting police officers.

The growing extradition controversy underscores growing unease over what is seen as increasing Chinese political influence in local affairs and worries the Hong Kong government has little recourse but to accept it.

In 2014, Hong Kong was shaken by rallies calling for a greater local say in how the territory's chief executive, the top official, is elected. Under the current system, only figures acceptable to the Chinese central government can run for the office.

Local pro-democracy group Demosisto, which played a leading role in the protests five years ago, said in a statement Sunday that it was launching a "peaceful" sit-in outside the Legislative Council in a bid to block the block the plan.

Opponents of the plan say that Hong Kong's autonomy, guaranteed for at least 50 years under a Sino-British agreement negotiated ahead of the handover on July 1, 1997, is in danger of further erosion .