TOKYO • Japan may have underpaid billions of yen in unemployment benefits after it emerged that the government has been collecting labour market data incorrectly for as long as 15 years.

Officials are supposed to gather data from all firms with 500 or more employees but in Tokyo, only about one-third of 1,400 such firms were surveyed, according to a civil servant at the Labour Ministry.

Labour Minister Takumi Nemoto has ordered a thorough investigation but admitted that he received a report about the problem as early as Dec 20.

This means the ministry published data it knew had sampling problems, undermining confidence in data from the world's third-biggest economy.

According to public broadcaster NHK, the problems could date back as far as 2004.

A ministry official, speaking on condition of anonymity, told Agence France-Presse the problem could have resulted in underpayment of unemployment benefits and industrial injury insurance benefits. Citing government sources, local agency Kyodo News said the budget may have to be reworked if benefits are paid back retroactively.

The monthly labour survey serves as a key indicator of the country's employment conditions, and is closely watched by the government and the Bank of Japan as a clue for their economic policy decisions.

AGENCE FRANCE-PRESSE