TOKYO (AFP) - A mystery gripping Japan over anonymous cash gifts has taken a new twist. For those who want the next batch of giveaways, the place to look is in their mailboxes -- or even right at their feet.

Residents of a Tokyo apartment building are baffled after a total of 1.81 million yen (15,210 dollars) was found in 18 mailboxes by Saturday, a police spokesman said.

"The money was in identical plain envelopes, which were unsealed and carried no names or messages," the spokesman told AFP.

But residents became "spooked" rather than pleased with the anonymous gifts -- and were too upright to pocket the money secretly.

"Some people initially suspected they were fake bills. When they realised the bills were real, they reported them to us," the spokesman said.

The predominantly middle-class apartment building in Tokyo is not alone. An envelope with one million yen was left in the mailbox of a 31-year-old woman in the western city of Kobe on Wednesday.

Police admit they have no idea who is leaving the cash -- whether a few people are behind the bizarre giveaways or if Japan is witnessing a craze of copycat benevolence.

Since June, dozens of city halls and other public buildings across the country have reported finding neatly packaged envelopes full of cash in men's restrooms.

The bathroom money has come with identical letters asking people to do good deeds -- leading to speculation that the benefactor may be a public servant trying to cheer up his profession or perhaps a member of a new-age religion.

Japanese cash dropoffs are not always so neat.

On Wednesday, bills worth 960,000 yen were inexplicably seen "falling" in front of a convenience store.

"We can just say the money came from the skies," a puzzled police official said. "There were other passers-by outside and customers in the store but the incident caused no confusion," he said.

"People thought it was too eerie to touch."

A man who contacted police saying his daughter had dropped the money had his claim rejected as groundless, the official said.

The largest single dropoff so far was in the ancient city of Kyoto on July 23, astonishing a 67-year-old woman who found an envelope containing 10 million yen of stacked bills in her mailbox.

But mystery money does not always reach police intact.

A woman walking on a bridge over Tokyo's Sumida River told officers that she saw bills falling at her feet from an elevated expressway above on July 6.

She believes 30 to 40 notes fell but police managed to collect only six notes worth 46,000 yen by the time they arrived.

"Some people were picking the money up on the bridge," the Tokyo Shimbun quoted the woman as saying.

No one can say if more people have collected money and not told police.

Media tallies suggest more than four million yen, including some found last year, has been found in the public restrooms.

Dutifully, police are holding most of the money in case the rightful owner eventually decides to reveal their identity.

current mood: amused