Yesterday, Mitsubishi issued a statement saying it had discovered that fuel consumption tests for roughly 600,000 of its vehicles had been run improperly, and therefore did not meet requirements under Japanese law, to give better results.
The affected vehicles are the Mitsubishi eK Wagon and eK Space, and the Nissan Dayz and Dayz Roox. The company has already halted production on the four cars.
BBC News reported that a Japanese official had called this an "extremely serious case" and given the company until 27 April to submit a report on the extent of the inaccurate testing.
"Based on [the findings from] the raid, and a report from the company, we would like to reveal the extent of the inaccuracies as soon as possible," said Yoshihide Suga, Japan's chief cabinet secretary. "We will deal with the situation in a strict manner and would like to make sure of the safety of cars."
In yesterday's statement, the company revealed that it was consulting external experts and would be producing its own report into the incident in due course.
Shares in Mitsubishi did not trade today but the Tokyo Stock Exchange pegged the closing price at ¥583, the equivalent to closing down 20.5 per cent.
Towards the end of last year, car manufacturer Volkswagen came under scrutiny, after confessing to rigging its carbon emissions results on some of its vehicles.
Mitsubishi declined to comment.