Japan is both aging and shrinking as it tries to emerge from two decades of economic stagnation. The construction workforce is a prime example.

It has contracted by a third since its peak in 1997 and is set to continue that trend - a fifth of the workers in that industry are over 60.

Yet construction companies face boom times with new building projects tied to the 2020 Tokyo Olympics and rebuilding work in the areas of northern Japan destroyed by the 2011 tsunami.

The easy answer would be to open the immigration gates to foreign labor, but the Japanese public, worried about safety and the impact on their culture, are adamantly opposed. Prime Minister Shinzo Abe has found a halfway measure - expanding a controversial program that offers "trainees" from China and elsewhere work for up to three years in the world's third-largest economy.

The plan, to be unveiled later this month, contemplates letting trainees stay for up to five years, relaxes hiring rules for employers and would boost the number of jobs open to them.

It follows a government decision in April allowing construction workers who had completed their stint under the trainee program to come back for another two to three years as regular laborers.

While the Japanese government says it doesn't have a specific target for the number of workers it wants to attract, the reforms amount to the biggest opening to foreign labor in many years.

Abe's economic plan specifically states that the enlargement of the program is not, however, an "immigration policy".

Abe's Liberal Democratic Party wants to strengthen the governance of the program with harsher penalties for companies that abused workers, and would rely on external inspectors and local governments to monitor compliance.