Local media reports showed investigators from the Ministry of Land, Infrastructure, Transport and Tourism entering offices of the company's assembly plant in central Japan's Nagoya today.
Yesterday, the company apologised for what it said was intentional falsification of mileage test data that falsely boosted fuel economy by about 5 per cent to 10 per cent.
Trading in Mitsubishi Motors' shares halted before the close today after the shares fell more than 20 per cent.
The inaccurate tests by the Tokyo-based automaker involved so-called "minicars" with tiny engines whose main attraction is generally great mileage. Mitsubishi was reporting mileage of up to 30.4 kilometers per litre.
The inaccurate tests by the Tokyo-based automaker involved 157,000 of its own-brand eK wagon and eK Space light passenger cars, and 468,000 Dayz and Dayz Roox vehicles produced for Nissan Motor Co.
All are so-called "minicars" with tiny engines whose main attraction is generally great mileage. They were produced from March 2013.