After last year's Fukushima nuclear disaster, a subcontracting company working to clean up the plant told workers to lie about high radiation exposure in a bid to maintain its contract, Japanese media reported on Saturday.

According to the new reports, an executive at the company told about 10 of its workers to place lead casing around their radiation detection devices, worn on their clothes, so the meters would appear to read under the radiation exposure threshold.

Several workers at the company, Build-Up, told the Asahi Shimbun newspaper that a senior on-site supervisor urged workers to manipulate the radiation monitors.

The workers had a recording of their meeting, Asahi reported.

"Unless we hide it with lead, exposure will max out and we cannot work," the executive told the workers.

The supervisor executive told the workers they would quickly surpass the legally permissible exposure limit of 50 millisieverts, and should lie to keep on working.

Japan's health ministry has said it will begin an investigation into the reports.