Shinzo Abe, the Japanese prime minister, was facing questions as it emerged the country is set to admit up to 340,000 foreign workers in a desperate bid to offset its declining work force.

Some of Mr Abe's own supporters expressed concern that a wave of foreign workers could lead to a jump in crime, and place too much strain on the social security system.

Mr Abe announced plans to increase the number of workers from abroad but did not give a figure.

However, between 260,000 and 340,000 could arrive over five years from 2019, Kyodo News reported.

It would be a dramatic shift in immigration policy for Japan.

Mr Abe plans an amendment to immigration law which would include a new visa for foreign workers with "specified skills."

It could mean up to 47,000 arriving in 2019, if the amendment passes the Japanese parliament next month.

Mr Abe said estimates would be released soon for a maximum number of foreign workers in each of more than a dozen industries, including farming and nursing.

He told the Japanese parliament: "Barring a significant change in circumstances we won't accept workers beyond these levels.

"Unless circumstances drastically change we won’t accept more workers than shown by the estimated figure. In that sense it’s a cap."