Around 15 billion euros ($16.9 billion) was wiped off the market value of Volkswagen AG on Monday following revelations that the German carmaker rigged US emissions tests for about 500,000 diesel cars.
By mid-afternoon trading in Frankfurt, Volkswagen's share price was down a stunning 18.1% at a near three-year low of 132.15 euros. Its dramatic fall weighed heavily on Germany's main stock index, the DAX, which underperformed its peers in Europe.
Volkswagen's market woes on Monday followed a weekend that saw the company's reputation for probity seriously damaged by revelations from the Environmental Protection Agency in the US that it had skirted clean air rules. All told, the EPA indicated that VW faces fines that could run up to more than $18 billion.
The EPA said VW used a device programmed to detect when the cars are undergoing official emissions testing. The software device then turns off the emissions controls during normal driving situations, allowing the cars to emit more than the legal limit of pollutants.
Volkswagen marketed the diesel-powered cars, which account for about 25% of sales, as a better option for the environment. The cars, built in the last seven years, include the Audi A3, VW Jetta, Beetle, Golf and Passat models.
"The company will have to recall nearly 500,000 affected cars, which will cost it millions of dollars, and that's even before the damage to its brand and potential fines," said Michael Hewson, chief market analyst at CMC Markets.
The agency has ordered VW to fix the cars at its own expense but said car owners do not need to take any immediate action. The EPA insisted that the violations do not pose any safety hazard and said the cars remain legal to drive and sell while Volkswagen comes up with a plan to recall and repair them. However, it said the cars posed a threat to public health.
The EPA also indicated the scale of the fines that could be imposed on VW. It said the carmaker could be hit up to $37,500 per vehicle for the violations -- a total of more than $18 billion. The California Air Resources Board is also investigating.
Volkswagen has had a difficult year, its share price having fallen from over 250 euros amid signs of faltering sales in the US and China.
VW edged out Toyota to become the world's top-selling automaker the first half of 2015. But a hit to its reputation from the emissions revelations could hamper its efforts at a sales rebound in the US.
If other regulatory authorities decide VW has a case to answer, then the carmaker faces the potential for even bigger fines.
"The news so far revolves around the US impact, but if European investigators become interested the potential penalties could multiply very quickly," said Chris Beauchamp, senior market analyst at IG.
A spokesperson for Germany's environment ministry said that, for now, authorities there were waiting to see how the US investigation develops.
"The auto manufacturers have to work closely with US authorities to comprehensively clarify the matter," Michael Schroeren told reporters in Berlin. "We expect reliable information from the car manufacturers so that (German authorities) can check whether comparable manipulation has happened in Germany or Europe."
Government spokesperson Steffen Seibert declined to comment directly on the case, but said Germany's standing as a leader in environmental protection hadn't been harmed.
"Our climate policy stands for itself and I think it's internationally recognised that Germany is one of the drivers on the way to (the international climate summit in) Paris," he said.