Hong Kong police can now demand phone or computer passwords from those who are suspected of breaching the wide-ranging National Security Law (NSL).
Those who refuse could face up to a year in jail and a fine of up to HK$100,000 ($12,700; £9,600), and individuals who provide "false or misleading information" could face up to three years in jail.
It comes as part of new amendments to a bylaw under the NSL that the government gazetted on Monday.
The NSL was introduced in Hong Kong in 2020, in wake of massive pro-democracy protests the year before. Authorities say the laws, which target acts like terrorism and secession, are necessary for stability - but critics say they are tools to quash dissent.
The new amendments also give customs officials the power to seize items that they deem to "have seditious intention".
