French carmaker Renault said fraud investigators had inspected three of its sites to look into its vehicle emissions technology - news that wiped billions off its market value in an echo of the scandal engulfing German rival Volkswagen.
Renault said investigations to date had found "no evidence of a defeat device equipping Renault vehicles", in a reference to a type of software program Volkswagen was found to have used by US investigators to cheat emissions tests.
French Energy Minister Segolene Royal, who had ordered tests for emissions technology on French and foreign-made cars, said that there was no sign of fraud by Renault.
"Shareholders and employees should be reassured," she told reporters, adding that defeat-device software had been found only on VW cars and no other brands.
However, preliminary results from the tests also showed that emissions exceeded limits on vehicles made by Renault and by some foreign carmakers, Royal added. She also said other manufacturers in France had been visited by the fraud investigators.
Renault shares fell as much as 22 per cent after union officials first said the sites had been searched, prompting the company to issue a statement confirming the inspections.
It said fraud investigators were looking at the way it uses exhaust emissions technology in an additional inquiry of parts and factories that follows an earlier investigation by the French government.
Volkswagen last year admitted to using software to conceal the level of toxic emissions from some of its diesel vehicles in the United States.
It faces billions of dollars in claims from owners of vehicles with similar software installed around the world.
The case has prompted investigations across several countries into Volkswagen, as well as checks on other car manufacturers and a tightening of emissions regulations which some industry analysts think could hit the entire diesel vehicle industry - a key market for Renault.
The French company saw some 5 billion euros erased from its market capitalisation in the worst day since its shares were first listed in 1994, according to Reuters data. The shares pulled back from their losses in heavy trading after the statement to close down 10.3 per cent at 77.75 euros.
"It's hard to believe that VW would have been the only one to have rigged emissions testing," said Clairinvest fund manager Ion-Marc Valahu, adding that he had sold out of his shares in European carmakers.
A government-mandated independent commission is conducting tests on 100 vehicles made by French carmakers, with 25 from Renault to be checked - equivalent to its French market share.
As of the end of December, four Renault vehicles out of a total of 11 had been tested and no signs of defeat technology had so far been discovered, the company said.
A member of the commission, Green lawmaker Denis Baupin, said Renault would address the panel next week about how to remedy the over-limit emissions detected in its cars.
"Renault's test clearly revealed anomalies and it's not by chance that fraud investigators decided to probe Renault," Baupin told Reuters.
The company said in a statement fraud investigators had "decided to conduct an additional investigation on parts and sites with the aim of definitively validating the initial analysis by the independent technical commission."
It added that its corporate headquarters and two technical sites had been targeted by the searches and that employees were fully cooperating.
The share plunge comes at a bad time for the French government's plans to pare back its Renault stake from 19.7 per cent to 15 per cent under a deal that brought to an end a dispute over control with the company's Japanese partner Nissan.
After shares of other carmakers began to be impacted by the news, rival French group PSA Peugeot Citroen said its offices had not been searched and that emissions tests had indicated no anomalies.
German carmaker Daimler said diesel engines that Renault supplies for its Mercedes-Benz brand do not contain defeat devices used to cheat on emissions tests.
A German environmental group said in November Renault's popular Espace minivan released toxic diesel emissions 25 times over legal limits in a Swiss study, despite complying with EU tests which it said were carried out at unrealistically low engine temperatures. Renault contested the findings.