A fugitive billionaire has vowed to launch a legal challenge against Hong Kong's controversial plan to sign an extradition agreement with Macau, Taiwan and mainland China, his lawyers said Monday.

He remains a free man because Hong Kong and Macau do not currently have an extradition agreement.

Hong Kong's government has recently announced plans to overhaul its extradition rules, allowing the transfer of fugitives with Taiwan, Macau and mainland China on a "case-basis" for the first time.

The proposal has sparked large protests and mounting alarm within the city's business and legal communities who fear it will hammer the financial hub's international appeal and tangle people up in China's opaque courts.

Lau has applied for leave to legally challenge the government's extradition proposal, according to a court application obtained by AFP, which also states that he has fled Hong Kong.

"The Bill, once enacted, would hang over those it affects like a cloud," Lau's lawyers wrote in the application filed in the city's High Court.

"The spectre of immediate detention if the Bill is enacted in its present form, and thereafter possibly even extradition to Macau to serve a manifestly unjust sentence, has compelled the applicant to exile himself from Hong Kong," it added.

The application asks the court to declare that any extradition agreement cannot be applied retroactively and argues that the city's leader Carrie Lam is being granted too much discretionary power to decide cases under the proposal.

Thousands of protesters hit the streets of Hong Kong on Sunday to demonstrate against the new extradition proposal, which will be discussed in the city's legislature on Wednesday.

Even a number of pro-Beijing politicians and prominent businesspeople have joined a growing chorus of opposition, while Taiwan's Mainland Affairs Council said it may issue travel warnings if the extradition agreement included China.

The proposal comes at a time of roiling distrust over how Beijing wields its authoritarian legal system -- and as two Canadian nationals languish in Chinese custody following the arrest of a top Huawei executive in Vancouver.

The Hong Kong government backtracked last week under pressure and exempted nine primarily economic crimes from the list of offences that could be covered by the new extradition law.

(This story has not been edited by Business Standard staff and is auto-generated from a syndicated feed.)