TOKYO - Japan's labour ministry has released monthly jobs data despite knowing that they did not satisfy sampling standards and they were erroneous, officials said on Tuesday (Jan 8).

According to Kyodo News, the revelation could undermine confidence in the accuracy of key economic indicators as Japan enjoys a prolonged phase of economic expansion.

Under existing rules, the ministry has to gather data from all companies with 500 or more employees. But it covered only a third of the roughly 1,400 businesses in Tokyo that should have been surveyed.

The monthly labour survey for October was released on Dec 7. The ministry released its revised version on Dec 21 but did not reveal that its data-gathering was inappropriate, Kyodo News said.

Speaking at a news conference, labour minister Takumi Nemoto said the problem was reported to him on Dec 20, adding that he has instructed officials to find out why the latest incident took place.

The monthly labour survey serves as a key indicator of the country's employment conditions, covering over 30,000 business establishments across Japan, also including selected ones with less than 500 workers.

Employment conditions are closely watched by the government of Prime Minister Shinzo Abe and the Bank of Japan, as wage growth is vital for Japan to break with deflation. The job market is tight due to an acute labour shortage while wage growth has been modest.