The oldest person in the world, Kamato Hongo, has celebrated her 115th birthday.

Mrs Hongo, who sleeps for two days and stays awake for two days, slept through the morning of her birthday, but was to celebrate with her family in southern Japan in the afternoon, according to media reports.

She is bed ridden and requires continual care, but apart from being slightly hard of hearing, she is otherwise said to be in good health.

Healthy Japan

Average female life is 84.93 years Male life expectancy is 78.07 years 17,394 people over the age of 100 84% of centenarians are women

She enjoys a tipple of sake, or Japanese rice wine, and uses her arms to perform the traditional dances of her native Tokunoshima island off Kagoshima prefecture in the south of the country.

Mrs Hongo now lives on the southern island of Kyushu and has seven children and more than 20 grandchildren. She has already outlived her eldest daughter, who died two years ago in her 90s.

"If you think about it really, its incredible," one of her daughters, Shizue Kurauchi, told Japanese media when the town major came to visit a couple of days ago.

"I mean, I've been taking care of her before she even turned 100 and every year I worry whether she'll be there the following year - even though she's always in fine health."

Mrs Hongo was recognised by the Guinness Book of Records as the oldest living person in March, after the death of Maud Farris-Luse, who died aged 115 in Michigan in the American Mid-West.

Japan's elderly

Appropriately Mrs Hongo's birthday fell this year on Japan's Respect for the Aged Day holiday.

The world's oldest man is also Japanese. Yukichi Chuganji, who is 113 years old, also lives in Kyushu.

Japanese have the longest life expectancy in the world. Their diet of fish and green vegetables are thought to contribute to their longevity.

Whilst Japan's high proportion of elderly is testament to its society's healthy diet, the greying population places a heavy burden on Japan's pension system.