The Office of the Communications Authority today announced that mobile network operators in Hong Kong have started to send voice or text alerts to mobile service users who receive incoming calls from a phone number prefixed with "+852", informing them that such calls are from outside Hong Kong.

The department has been working closely with telecommunications service providers and law enforcement agencies to devise and roll out various technical measures in combating fraudulent calls and messages delivered through telecommunications networks.

The introduction of the voice or text alert for incoming "+852" calls is the latest measure launched by the telecommunications industry this month, which aims to combat improper use of telecommunications for illicit purposes and raise public awareness of suspicious calls originating from outside the city.

The new measure will be fully implemented by all mobile service providers from May 1.

A standard alert message - "Call is from outside Hong Kong. Beware of deception." - will be sent to the mobile service user receiving an incoming "+852" call. The voice alert is spoken in Cantonese, Putonghua and English, while the text alert is written in English and Chinese.

The alert service is provided free of charge by mobile service providers. Users are not required to pre-register, install any mobile apps or make any changes to their phone settings.

The department reminded the public that even if the caller number display has no "+" sign and shows an 8-digit Hong Kong phone number, it may still be a scam call.

People should always stay vigilant when using telecommunications services and never disclose personal information or transfer money to unknown callers so as to protect themselves from losses, it added.