Hong Kong's Security Bureau said on Wednesday it would use powers in a new national security against six self-exiled activists residing in Britain, including cancelling their passports, after they fled the China-ruled city.

The six are Nathan Law, Christopher Mung Siu-tat, Finn Lau, Simon Cheng, Johnny Fok Ka-chi and Tony Choi Ming-da. City authorities put them on a wanted list last year.

"These lawless wanted criminals are hiding in the United Kingdom and continue to blatantly engage in activities that endanger national security," the bureau said in a statement.