The world's oldest person is set to celebrate her 117th birthday, but says that despite her age, her life has seemed rather short.

Misao Okawa was born in Osaka, Japan, on March 5, 1898, was recognized as the world's oldest person by Guinness World Records in 2013.

Mrs Okawa said she still does not know how she has lived for so long, but has previously credited her longevity to eight hours sleep, eating sushi, and doing squats until the age of 102.

'It seemed rather short,' she said after an Osaka government official asked how she felt about living for 117 years, adding that she is 'very happy' to be that age.

Asked for the secret of her longevity, the great-grandmother responded nonchalantly, 'I wonder about that too.'

During the celebrations of her 116th birthday last year, Mrs Okawa said: 'Eat and sleep and you will live a long time. You have to learn to relax.'

The head of Mrs Okawa's retirement home added that she 'eats three large meals a day, sleeps eight hours a night, and insists that her favourite meal is sushi, particularly mackerel on vinegar-steamed rice.'

The great-grandmother has slowed in recent months and has trouble hearing but she eats well and is in good health, the Osaka care home said today.

Mrs Okawa married her husband, Yukio, in 1919, and they had three children — two daughters and a son.

Mrs Okawa says that the happiest moments of her life were her wedding and the birth of her children – she still has a surviving son and daughter who are now 94 and 92.

She now has four grandchildren and six great-grandchildren. Her husband died in 1931.

Mrs Okawa was recognized as the world's oldest person by Guinness World Records in 2013. Experts say it is no surprise that Mrs Okawa is Japanese.

The nation has the most centenarians in the world, with more than 58,000, according to the government. About 87 percent of them are women.

They say it is down to an excellent healthcare system, encouragement to stay active in old age and a healthy diet made up of fish, rice and fruit.

The life expectancy for a Japanese woman is almost 86 years while the average for a Japanese man is 79.6 years.