A city in Japan has begun tagging people who have dementia with QR codes that can be scanned by authorities if they get lost.

A company in Iruma, north of Tokyo, developed tiny nail stickers, each of which carries a unique identity number to help concerned families find missing loved ones, according to the city's social welfare office.

The adhesive QR-coded seals for nails, part of a free service launched this month and a first in Japan, measure just one centimetre in size, AFP reported.

“Being able to attach the seals on nails is a great advantage,” a city worker said.

“There are already ID stickers for clothes or shoes but dementia patients are not always wearing those items.”

If an elderly person becomes disorientated, police will find the local city hall, its telephone number and the wearer's ID all embedded in the QR code.

The chips remain attached for an average of two weeks, even if they get wet, the official said, citing recent trials.

Japan is grappling with a rapidly ageing population with senior citizens expected to make up 40 per cent of the population by about 2060.

Last month, Japanese police started offering noodle discounts at local restaurants to elderly citizens who agreed to hand in their driving licences.