Hong Kong authorities have defended legal changes that have made it illegal to withhold smartphone passwords from police in national security investigations, after the United States sent a new alert to its citizens travelling to the city.

Its strongly worded response came after the US consulate in Hong Kong issued a new security alert reminding Americans that it was now a criminal offence for anyone to refuse giving local police the passwords or decryption assistance to access all personal electronic devices including mobile phones and laptops.

“This legal change applies to everyone, including US citizens, in Hong Kong, arriving or just transiting Hong Kong International Airport,” the alert read. “In addition, the Hong Kong government also has more authority to take and keep any personal devices, as evidence, that they claim are linked to national security offences.”

Anyone who refuses to comply faces a maximum penalty of one year in prison and a HK$100,000 (US$12,800) fine, according to the revised rules.

Providing false or misleading information is punishable by up to three years’ imprisonment and a HK$500,000 fine.

A spokesman for the Hong Kong government stressed that under normal circumstances, police must have reasonable grounds to suspect that an electronic equipment may contain evidence of a national security breach, and must obtain authorisation from a magistrate before they can search the device or require a person to unlock it.