The remains of a Japanese woman have been found in a backpack, in the latest gruesome discovery by investigators searching for missing old people.

The woman's son told police his mother died in 2001 but he had not been able to pay for a burial.

A similar discovery weeks ago sparked a search for people who are registered as being more than 100 years old.

According to Japanese media, the audit has so far identified 281 centenarians who are missing or have already died.

The inquiry followed the discovery last month of the mummified remains of a man registered as being 111 years old. He had died 30 years earlier.

Those unaccounted for include a 125-year-old woman whose registered address was turned into a park in 1981, according to media reports.

In the latest find, a 64-year-old man told officials that his mother had died at home in Tokyo in "about June 2001".

"Because I didn't have money for a funeral, I didn't report her death," the Sankei Shimbun newspaper quoted him as saying.

The AFP news agency reported that he told police: "I laid out her body for a while, washed it in the bath, then broke up the bones and put them into a backpack."

But the woman's pension continued to be paid and police are now investigating the son on suspicion of fraud.

There are more than 40,000 registered centenarians in Japan, according to government data, but the number of missing has raised concerns that the welfare system is being exploited by dishonest relatives.

There are more than 40,000 registered centenarians in Japan

There was a show recently that said some scientists suspect there are people in their 50s and 60s now who could live to see 150