(Bloomberg) -- The U.K. is granting the most special travel documents to Hong Kong residents since the 1997 handover, bolstering predictions of a mass exodus as China tightens its grip over the former British colony.

Some 216,398 Hong Kong residents received British National (Overseas) passports during the first 10 months of the year, higher than any annual figure stretching back to 1997, according to data provided by the U.K.’s Passport Office under the Freedom of Information Act.

In October alone, the office issued 59,798 Hongkongers with BNOs, or 52% higher than in the same period last year, and the highest monthly figure since the Passport Office began readily compiling them in 2015. That translates to more than five every minute, based on an average eight-hour working day.

The numbers, which also include renewals, provide the latest glimpse of the departures Hong Kong faces as this year’s sudden enactment of a national security law — in response to the mass anti-Beijing protests last year — raised concerns about dwindling freedoms in the Asian financial hub.

The monthly numbers began spiking up in July, when the U.K. upgraded the status of BNO passport holders. They can now stay in Britain for five years and have an easier path toward U.K. citizenship.

China has criticized the U.K.’s move to invite more Hong Kong residents to its borders as an inappropriate interference in the country’s domestic affairs. The Chinese Foreign Ministry said in July that the country might not recognize BNO passports as valid travel documents, although that would likely have little practical significance for Hong Kong residents, who usually enter and exit the city using their local identity cards.

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Meanwhile, real estate agents in London have been seeing a surge in interest from Hong Kong, with inquiries up almost 80% this year for some agencies.

There are an estimated 2.9 million Hongkongers eligible for BNOs and as many as 2.3 million of their dependents, according to a U.K. government study. Of those eligible, the U.K. estimates as many as 322,000 will move to the country between 2021-2025.

The Hong Kong government’s Information Services Department didn’t immediately respond to a request for comment.

The BNO identity document is a product of the British colonial era that ended in 1997. It was made to recognize Hong Kong residents of the time as overseas British nationals, but only gave holders the right to visit the country for as long as six months.

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