Munich - German prosecutors on Thursday said they had opened a preliminary inquiry into allegations that BMW used a defeat device to cheat diesel emissions tests in at least one of its models.

It comes after environmental group DUH this week said tests carried out on a 2016 BMW 320d showed the car emitted higher harmful nitrogen oxide (NOx) levels on the road than in the lab, and well beyond legal limits.

"Investigators have begun a preliminary probe" into possible irregularities in BMW's emissions control systems, a spokeswoman from the Munich prosecutor's office told DPA news agency.

"Since there's nothing wrong with the cars, we expect that we have nothing to fear," a BMW spokesman told AFP.

The Bavarian carmaker has insisted its vehicles pass all regulatory tests, accusing DUH of subjecting the car to "atypical driving conditions".

DUH chief Juergen Resch told reporters on Tuesday there were "very strong indications" BMW had installed a cheating device in the tested model.

A preliminary investigation is used by prosecutors to determine if there is enough evidence to suggest a crime has been committed.

It is not on the same level as a formal investigation.

The German transport ministry has also said it will look into the allegations made by DUH.

The controversy marks the latest fallout from the 'dieselgate' scandal that erupted when Volkswagen admitted in 2015 to using cheating software in 11 million diesel cars worldwide to dupe pollution tests.

Suspicions have since spread to other carmakers and cast a pall over Germany's vaunted auto industry, which produces around one in five vehicles sold worldwide.

Volkswagen is still grappling with the fallout from the scandal, which has so far cost the auto giant more than 25 billion euros (R404bn) in fines, compensation and recalls.

A US court on Wednesday sentenced former VW executive Oliver Schmidt to seven years in prison for his role in the scam, after he pleaded guilty to conspiracy to commit fraud and violating the US Clean Air Act.

Meanwhile, EU lawmakers on Thursday agreed to upgrade the bloc's legislative arsenal on approving new vehicle models.

The Commission, Europe's executive body, will be handed the power to fine carmakers up to 30 000 euros (R485 000) per non-conforming vehicle.

Agence France-Presse