About a dozen of Japan's 47 prefectures began Friday to mail 12-digit identification numbers to residents in the country under the new My Number social security and tax number system.

The government plans to send the numbers to all of the approximately 55 million households in Japan by the end of November before the numbers begin in January to be used for tax, social security and disaster fields.

The numbers will be written on mailed paper cards, accompanied by written applications for personal ID cards to be issued as requested by residents from January.

Employees will be required to provide their numbers to their employers to be put on tax withholding certificates and other documents from next year.

Residents will have to use their numbers for some administrative procedures, including applications for welfare benefits.

The My Number law took effect in early October to allocate 12-digit identification numbers to everybody with resident registry in Japan, including foreign nationals, to enable tax and other authorities to discover tax evasion and wrongful receipt of welfare benefits more easily while simplifying administrative procedures for residents.

But concerns have grown over the government's handling of personal information under the system after massive personal data leaks from the Japan Pension Service following cyberattacks in May.