The Japanese government on Friday said it would release a fifth of its emergency rice stockpile after hot weather, poor harvests and panic buying over a "megaquake" warning nearly doubled prices over a year.

Japan has previously tapped into its reserves to cope with disasters, but this marked the first time since the stockpile was built in 1995 that it was doing so because of supply chain problems.

Some supermarket shelves were emptied in August of rice following a week-long holiday, a series of typhoons and warnings of a looming major earthquake that has so far failed to materialise.

The government had initially hoped prices would stabilise late last year once newly harvested rice arrived in stores, but inflation continued unabated, this time because some distributors were hoarding for fear of running out.

Agriculture Minister Taku Eto told reporters on Friday the government would release 210,000 tonnes of rice from its stock of one million tonnes.

"I hope you will take this as our strong determination to improve at all costs the situation where distribution has been delayed and stuck," he said.

Rice prices had already began to change consumption patterns for some like Tokyo resident Eriko Kato.

"I still do buy rice occasionally, but since it's so expensive I sometimes give up on buying it once I see the price," Kato, 41, said.

A five-kilogramme bag was retailing at 3,688 yen (US$24) in the last week of January, according to a government survey, up from 2,023 yen last year.

Rice consumption in Japan has more than halved in the past 60 years to about 50.9 kilos in 2022, but the grain remains deeply ingrained in Japanese culture and its harvesting has shaped the nation's landscape -- even being used in Shinto rituals. (AFP)