Mitsubishi Motors Corp's (7211.T) shares were untraded on Thursday as they were swamped with sell orders, and were poised to hit a record low after the Japanese automaker admitted to manipulating fuel-economy data.

Japan's sixth-biggest automaker said on Wednesday it had manipulated test data to overstate the fuel economy of 625,000 cars, a situation the government called "extremely serious".

Mitsubishi Motors had said it stopped making and selling its eK mini-wagons for the domestic market after Nissan Motor Co (7201.T), which markets a similar model made by Mitsubishi Motors, found a discrepancy in fuel efficiency test data.

JPMorgan auto analyst Akira Kishimoto estimated the cheating could cost Mitsubishi more than 50 billion yen ($450 million), including payments to consumers, the costs of replacing parts, and compensation to Nissan.

And while Mitsubishi said the cars were sold only in Japan, the impact could be felt wider.

"In addition to the costs of the scandal, the secondary effects on worldwide sales could be very large," Kishimoto wrote in a note to clients, adding that the automaker has tied its brand to environmentally friendly technology with its fuel-sipping plug-in hybrids and fully electric vehicles.

Under Tokyo stock market rules, if no trades are made in Mitsubishi Motors' shares for all of Thursday, they will be deemed to have closed at the indicated price. 

The indicated price on Thursday was 583 yen, the lowest they can go for the day, representing a 20 percent drop from Wednesday's close.

A fall to that level would take Mitsubishi Motors' shares below the previous record low of 660 yen and would mean they have lost a third of their market value, or $2.5 billion, in two days.

Revelations of the cheating follow a cover-up scandal that brought Mitsubishi close to the brink about a decade ago, when the automaker admitted to systematically concealing defects over decades. It was Japan's worst automotive recall scandal at the time.

"This undermines consumers' trust and it shouldn't have happened. It is an extremely serious case," Chief Cabinet Secretary Yoshihide Suga, the government's top spokesman, told a news conference.

"We want the whole picture of the misconduct clarified as soon as possible, and want a strict response and the safety of automobiles to be ensured," he said.

Japan's transport ministry on Wednesday ordered the company to submit a full report on test manipulation within a week, and said it would decide on its response by May 18.

VOLKSWAGEN

Mitsubishi, which has annual sales of just over 1 million cars, is the first Japanese automaker to report misconduct involving fuel economy tests since Volkswagen AG (VOWG_p.DE) was discovered last year to have cheated diesel emissions tests in the United States and elsewhere.

People briefed on the matter told Reuters Volkswagen and U.S. officials had reached a framework deal under which the automaker would offer to buy back almost 500,000 diesel cars that used sophisticated software to evade U.S. emission rules.

South Korean car maker Hyundai Motor Co (005380.KS) and affiliate Kia Motors Corp (000270.KS) in 2014 agreed to pay $350 million in penalties to the U.S. government for overstating their vehicles' fuel economy ratings. They also resolved claims from car owners.