TOKYO -- Something strange is happening in Japan -- people are stumbling across piles of cash, often at garbage collection points. In 2016, the equivalent of $150 million was discovered and reported to the police.

With the country's population graying and families shrinking, more people are spending their twilight years living and dying alone. It seems a growing number of elderly are leaving behind stashes of money that family members are unaware of and sometimes trashing by mistake.

"It could have possibly belonged to a relative of mine," someone reported to the police shortly after a waste disposal company in Gunma Prefecture, central Japan, discovered 40 million yen ($356,000) in cash in a refuse pile in April. The man to whom the money originally belonged had died, and the legal heir had dumped the money by accident, according to the person who spoke to the police.

After a two-month investigation, the police concluded the money had indeed belonged to the deceased person in question. Establishing ownership was not easy. The authorities had to check the person's bank transaction records against the dates printed on strips of paper that bound the bank notes together. Stacks of notes worth 1 million yen are usually tied into bundles.

At the end of June, the money was returned to the relative, as the statutory deadline approached. If no one claims abandoned cash within three months, the money goes to the finder.

Similar cases have been reported in the media with surprising frequency. A waste disposal facility in Nara Prefecture, western Japan, reportedly found about 20 million yen in bank notes in May. Another 20 million yen or so was discovered in a food container at a garbage collection point at a historic hot spring in Isihikawa Prefecture, central Japan.

According to a police white paper, police received 17.7 billion yen in mystery cash in 2016, about 70% of which was returned to owners. The rest -- 5.3 billion yen -- remains unclaimed.

That is the biggest haul since 1991, when Japan's bubble economy was bursting. The amount of cash found has been rising steadily since 2010, with the exception of 2011, when a massive earthquake and tsunami hit northeastern Japan, reducing houses to rubble and washing safes out to sea.

In addition to growing numbers of elderly dying with unnoticed stashes, some people hoard cash at home, feeling safer with their money close at hand.

Dead assets

According to data from the Tokyo Medical Examiner's Office, 3,175 Tokyo residents aged 65 or older died alone last year, nearly twice the 1,650 who did so in 2004.

This has increased demand for house-clearing services. Tokyo-based One's Life earlier this year found two safes at the home of an elderly man who had died alone. "There is probably nothing valuable in these safes. Please throw them away," said a relative. But workers looked inside, just in case. They found 200 million yen in cash. In another instance, the company found 5 million yen in a closet drawer while clearing a house on behalf of a client.

"Visiting a bank can be physically tiresome for many elderly people, and they often want to keep cash at home," said Takako Uwano, head of One's Life. Uwano suggested people should not assume surviving family members will take care of their possessions after they die, but should make the necessary arrangements while they are alive. "It's important to make clear to loved ones what you have in the house, and where," Uwano said.