About 300,000 people are expected to leave Hong Kong for Britain using a new visa route which opens on Sunday.
Hong Kong's British National (Overseas) passport holders and their immediate dependants will be able to apply for the visa using a smartphone app.
About 7,000 people from Hong Kong have already been allowed to settle in the UK since July, the Home Office said.
The Chinese foreign ministry said from 31 January, it will no longer recognise the BNO passport as a travel document.
It will not be accepted as proof of identity either, China said, and they "reserve the right to take further measures".
The visa was announced in July after China imposed a new security law in Hong Kong.
Beijing has previously warned the UK not to meddle in domestic issues.
Prime Minister Boris Johnson said the move honoured the UK's "profound ties of history and friendship" with the ex-British colony.
Those who apply and secure the visa will be able to apply for settlement after five years and then British citizenship after a further 12 months.
https://www.bbc.co.uk/news/uk-55847572