A Japanese octogenarian was swindled out of thousands of dollars after falling in love online with a self-described astronaut who sought her help to avert a spaceship crisis, police said Tuesday.

The hapless woman in Japan's northern Hokkaido island met the fraudster in July on social media, who claimed to be a male astronaut, a local police officer told Agence France-Presse (AFP), describing the case as a "romance scam."

After some exchanges, the scammer one day told her he was "in space on a spaceship right now" but was "under attack and in need of oxygen," the official said.

The scammer then urged her to pay him online to help him buy oxygen and successfully hoodwinked her out of around 1 million yen ($6,700).

The woman lives alone and started developing feelings for him as their online communication progressed, local media, including Hokkaido Broadcasting, said, quoting investigative sources.

"If a person you met on social media ever demanded cash from you, please be suspicious of the possibility of a scam and report to the police," the official said.

Japan has the world's second-oldest population after tiny Monaco, according to the World Bank and older people frequently fall prey to various forms of organized fraud.

These include the classic "it's me" scam, where perpetrators impersonate family members in trouble to extract money from the victim.

Elderly people can also be cajoled into using ATMs to get non-existent "refunds" of their insurance premiums or pensions, police have warned.