Bounties placed on pro-democracy activists by Hong Kong show some of the "worst fears" are coming true after the imposition of a 2020 national security law, experts say.

The report covers July-December 2020, after the sweeping national security law was imposed on the city by Beijing in June last year.

"If China imposes [its] law, we will explore options to allow British Nationals Overseas to apply for leave to stay in the UK, including a path to citizenship," Home Secretary Priti Patel said in a statement.