TOKYO (AFP) - More than 28 per cent of Japan's population is now officially classified as elderly according to government data, the highest rate in the world as the first wave of post-war baby boomers enter old age.

Those aged 65 or older now make up a record 35.6 million, or 28.1 per cent of the total population, the government said on Sunday (Sept 16).

The proportion is the highest by far in the world, ahead of 23.3 per cent in Italy, 21.9 per cent in Portugal and 21.7 per cent in Germany, according to United Nations data for those countries.

The government also said those aged 70 or older accounted for 20.7 per cent of the population, surpassing 20 per cent for the first time.

The figures show the nation's post-war baby boomers are now entering old age, it said.

The demographic shift is due to a combination of a low birth rate and long life expectancy.

Japan's rapidly greying population poses a major headache for policymakers, who are faced with trying to ensure an ever-dwindling pool of workers can pay for the growing number of pensioners.