British Prime Minister Boris Johnson has promised to provide a path to British citizenship for potentially millions of Hong Kongers, as China prepares to impose a draconian new national security law on the city, EDNews.net reports citing CNN.

That law, Johnson said in an op-ed published in the South China Morning Post Wednesday, "would curtail (Hong Kong's) freedoms and dramatically erode its autonomy," contravening the Sino-British Joint Declaration which laid the groundwork for the city's handover from British to Chinese rule in 1997. Should it come to pass, the United Kingdom will "uphold our profound ties of history and friendship with the people of Hong Kong," by changing immigration laws to allow more Hong Kongers to settle and work in the country.

"This would amount to one of the biggest changes in our visa system in British history. If it proves necessary, the British government will take this step and take it willingly," Johnson said.

His announcement formalizes a proposal made by UK Foreign Secretary Dominic Raab last month to extend rights granted to holders of British National (Overseas), or BNO passports. At present, the some 350,000 people currently holding BNO passports can travel to the UK visa free for six months. The new system, Johnson said, will "allow any holder of these passports from Hong Kong to come to the UK for a renewable period of 12 months and be given further immigration rights, including the right to work, which could place them on a route to citizenship."

That idea has already been met with outrage by Beijing, which accused London of breaching its treaty obligations, even as a foreign ministry spokesman argued that the Sino-British Joint Declaration was "completely fulfilled" and no longer in effect.

"All Chinese compatriots residing in Hong Kong are Chinese nationals, whether or not they are holders of the British Dependent Territories Citizens passport or the British National (Overseas) passport," spokesman Zhao Lijian said last week. "China reserves the right to take corresponding measures."

In his op-ed, Johnson said it was China who was "in direct conflict with its obligations under the Joint Declaration, a legally binding treaty registered with the United Nations."

"Instead of making false allegations -- such as claiming that the UK somehow organized the protests -- or casting doubt over the Joint Declaration, I hope that China will work alongside the international community to preserve everything that has allowed Hong Kong to thrive," he said, referring to China's continued insistence that last year's pro-democracy demonstrations in Hong Kong were orchestrated by foreign agents.

Hong Kong and Chinese officials have argued that concern over the law is overblown, and defended it as necessary for targeting "terrorists" and separatists in the city. Speaking to CNN last month, Hong Kong's Chief Secretary, Matthew Cheung, said that "99.99% of the Hong Kong population will not be affected, they'll go about their lives, they continue their investment in Hong Kong."