A five-year UK visa will become available to Hong Kong citizens deemed British Nationals overseas, or BNOs, from Sunday with a path to citizenship, the British Home Office announced on Friday,  as the Chinese territory faces tighter control by Beijing under a Chinese National Security Law put in place last year.

"This new visa delivers on our promise to the people of Hong Kong, honoring our strong historic relationship and upholding their freedoms," said Home Secretary Priti Patel in a statement.

Britain introduced the visa in July following the enactment of the National Security Law, which severely limits dissent and freedom of speech in the city. Roughly 5.4 million people in the former British colony are eligible with the UK to start accepting applications online at 5 p.m. Hong Kong time on Sunday.

"I am immensely proud that we have brought in this new route for Hong Kong BN(O)s to live, work and make their home in our country," UK Prime Minister Boris Johnson said.

Many of those keen to leave Hong Kong cite hopes for greater economic and political stability. Britain's previous colonial hold of Hong Kong that ended in a 1997 handover of administration to China under a "One Country, Two Systems" formula with freedoms under Hong Kong's Basic Law and hailed by both sides at the time, is now seen in danger.

"China's imposition of the National Security Law in Hong Kong constitutes a clear and serious breach of the Sino-British Joint Declaration," Dominic Raab, the British Foreign Secretary, said in a statement on Friday.

But Chinese officials condemned Britain's continued involvement in Hong Kong.

"The British side, in breach of its promise, has chosen to obstinately and repeatedly hype up the BNO passport issue to interfere with Hong Kong affairs and China's internal affairs," Chinese Foreign Ministry spokesperson Zhao Lijian said on Thursday.

He warned the move would "only end up hurting its own interests" and reiterated China's commitment to Hong Kong: "No forces under whatever circumstances can erode the determination of the Chinese government and the Chinese people to [...] safeguard Hong Kong's prosperity and stability."

The UK expects between 123,000 and 153,700 passport bearers and their families will come in the first year, reaching up to 322,400 BN(O) status holders over the next five years.

This could trigger more than $36 billion in capital outflows in 2021 alone, according to a report by the Bank of America.

Already, approximately 7,000 BN(O) status holders and their dependents have been given 'leave outside the rules' at the border to enter the UK.