Japan's sixth-largest automaker by market value announced on Wednesday that it had manipulated fuel economy tests for about 625,000 vehicles and that it would halt production and sales of the affected models as well as launch a probe into cars sold overseas.

"We found that with respect to the fuel consumption testing data... [the company] conducted testing improperly to present better fuel consumption rates than the actual rates," Mitsubishi president Tetsuro Aikawa told a Tokyo news briefing.

Admitting that the testing method used by Mitsubishi was "different" from the one required by Japanese law, Aikawa added: "We express deep apologies to all of our customers and stakeholders for this issue."

The manipulations have been found in the mini-car models "eK Wagon" and "eK Space," as well as in the "Dayz" and "Dayz Roox" vehicles, which Mitsubishi produces for rival Nissan. They came to light after Nissan discovered inconsistencies in fuel economy data and reported them.

Stock plunges on VW fears

This is the first time a Japanese automaker has reported misconduct involving fuel economy tests since Germany's Volkswagen (VW) last year was discovered to have cheated on diesel emissions tests in the United States and elsewhere.

As a result, Mitsubishi shares nosedived on Wednesday, falling 15.16 percent and wiping $1.2 billion from its market value. The fall was its biggest one-day plunge since 2004, when the carmaker was struggling to launch a turnaround, after teetering on the edge of bankruptcy due to a lack of cash and a series of huge recalls.

Investors also sold the stock because they fear massive penalties and damage claims from customers and governments, similar to those currently hitting VW across the world. The German car titan has admitted to installing emissions-cheating software in 11 million diesel engines worldwide. The costs of the VW scandal are still incalculable but are expected to run into several billion dollars as a result of fines and lawsuits.

Mitsubishi's mini-cars, running on 660cc gasoline engines, are hugely popular in Japan, although they found little success abroad. But the automaker also produces the Outlander sport utility vehicle of which it has sold more than a million all over the world in its latest fiscal year.

"In order to conduct an investigation into these issues objectively and thoroughly, we plan to set up a committee consisting of only external experts. We will publish the results of our investigation as soon as it is complete," the Mitsubishi president announced Wednesday.

South Korean automakers Hyundai and Kia in 2014 agreed to pay $350 million in penalties to the US government for overstating their vehicles' fuel efficiency, and have resolved claims by customers.

uhe/kd (AFP, dpa, Reuters)