A crime wave targeting the elderly is threatening to change Japan's status as one of the safest countries in the world.

Every day about 30 people are being defrauded out of their life savings, in a new type of crime known as "it's me" fraud.

Police say it is Japan's number one crime problem.

Last December, Haruko Tanaka, who lives in northern Tokyo, received a desperate phone call from a person who she believed was her son.

"He said 'I've left money of my company's on a train and I need to replace it by this afternoon. So please Mum send me $40,000'," Ms Tanaka said.

She rushed to her local bank but the teller, acting on his suspicions, called the police. They checked with Ms Tanaka's son and discovered the caller was a fraudster.

The stories may differ slightly. It might be a traffic accident or "my girlfriend is pregnant", but they always manipulate the emotions and good intentions of parents or grandparents.

"I was in panic at that time," Ms Tanaka said. "I believed it was my son and what he said. It was sudden so I couldn't make a proper judgement."

Last year elderly people were defrauded of about $500 million in 12,000 cases.

This year the figures are on track to be even bigger.

Fraud creating new generation of criminals: police

Superintendent Ryuji Hatayama, head of Tokyo's special fraud taskforce, says it is proving difficult to investigate and arrest the ringleaders.

"This is low risk and high return for organised groups like the Yakuza," Superintendent Hatayama said.

"The leaders stay in safe locations and just make the calls, then they send out young men to collect the money but they are not told anything about the syndicate they are working for, so it's difficult to trace."

Police say "it's me" fraud is creating a new generation of criminals, enticing young people with promises of getting rich quick.

Superintendent Hatayama says university students and even high school students who were previously never involved in crime are being arrested for the first time.

"It's pushing Japanese society to a turning point ... whether we can keep our low crime rate or lose our safety," he said.

So far the police have arrested 1,200 perpetrators of the crime.

Last week Tokyo police caught one of the bosses, who is alleged to be part of a Yakuza gang that stole $500,000.

They posed as policemen over the phone to extract money from the elderly and sent boys to collect.

The police have started a nationwide education campaign, turning up at shopping malls and train stations with local volunteers handing out leaflets.

They are asking the elderly to check the identity of callers demanding money.

Bank employees are also being trained to be on high alert for potential fraudsters.