Britain will change its immigration rules and offer millions of people in Hong Kong “a route to citizenship” if China imposes new security laws, Boris Johnson has said.

Writing in the Times, Mr Johnson said the UK would “have no choice” but to uphold its ties with the territory.

China is facing mounting criticism over its planned law.

Many people in Hong Kong fear it could end their unique freedoms, which the rest of China does not have.

China’s new law: Why is Hong Kong worried?

The UK is already in talks with allies including the US and Australia about what to do if China imposes the new law – which would make it a crime to undermine Beijing’s authority – and people start fleeing Hong Kong.

In the Times on Wednesday, the prime minister confirmed that if China passes the law, people in Hong Kong who hold British National (Overseas) (BNO) passports will be allowed to come to the UK for 12 months without a visa. Currently they are allowed to come for six months.

Around 350,000 people in Hong Kong currently already have a BNO passport, but 2.6 million others are also eligible.

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A new wave of protests have taken place in Hong Kong over the national security law

Passport-holders would also be given further immigration rights, including the right to work.

This “could place them on a route to citizenship,” Mr Johnson said.

More about the BNO passport and what could change

‘Britain will not walk away’

The prime minister added that the immigration changes “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.

“Many people in Hong Kong fear their way of life, which China pledged to uphold, is under threat.

“If China proceeds to justify their fears, then Britain could not in good conscience shrug our shoulders and walk away; instead we will honour our obligations and provide an alternative.”