Japanese investigators visited a Mitsubishi motors facility Thursday in Nagoya after the company admitted to manipulating fuel efficiency data on more than 620,000 cars.
Japan's Chief Cabinet Secretary Yoshihide Suga said the government wants to "reveal the extent of the inaccuracies as soon as possible" and deal with the situation in a "strict manner."
Mitsubishi said unnamed employees were responsible for cheating the efficiency tests, making it seem like the cars got better fuel economy by up to 10 percent.
The vehicles are so-called mini-cars popular in Japan partially because of their gas mileage. Some affected models are ones that Mitsubishi manufactures for rival Nissan.
Mitsubishi's stock fell by another 20 percent Thursday, after declining 15 percent on Wednesday.
The scandal follows a similar case involving German car company Volkswagen, which is facing a lawsuit in the United States for selling cars with software to help them illegally pass emissions tests.