French car maker Renault's shares plunged by over 20% after anti-fraud investigators searched the offices of the company last week, apparently as part of a probe into emissions testing. Renault shares on the Paris stock exchange dropped to 21% at 12.30pm -- the biggest since 4 January, 1999, reports Bloomberg.

Renault confirmed that anti-fraud raids have taken place in the company but no cheating devices have been found in tests on diesel engines. Investigators visited four different sites near Paris, including Lardy and co. headquarters in Boulogne-Billancourt on 7 January, according to AFP.

Interestingly, the news regarding the plunge in Renault's shares also impacted the shares of the other manufacturers. The PSA Peugeot Citroen's stocks also fell by 7%; its offices had not been searched.

Many automakers are under scrutiny following the emissions scandal related to Volkswagen that came to light in September 2015. Volkswagen, the world's largest automaker by sales, landed in trouble when the US Environment Protection Agency said VW intentionally violated the Clean Air Act by using sophisticated software in its diesel-powered cars that detects emissions testing.

In the latest development on the scandal, Volkswagen plans to recall the concerned vehicles, with US regulators rejecting a strategy submitted on Tuesday. The official said the proposal did not adequately address the problem.