Staff at auto giant Volkswagen are under investigation for tax evasion in a case linked to the German company's massive emissions cheating scandal, prosecutors said Tuesday.

Public prosecutor Birgit Seel in the western city of Brunswick told AFP that her office had this week launched the probe against "five VW employees" at the group's headquarters in Wolfsburg.

She declined to comment on their job titles or areas of responsibility but said the investigation was tied to the pollution test affair.

The same prosecutor's office had earlier this month launched an investigation into allegations that Volkswagen lied about the carbon dioxide emissions of up to 800,000 cars.

The carmaker has admitted to fitting 11 million diesel engines worldwide with sophisticated software designed to skew the results of pollution tests for nitrogen oxide emissions.

That admission has triggered both regulatory and criminal investigations in several countries, including Germany and the United States, with VW facing the risk of having to pay billions in fines.

The so-called "defeat devices" turn on pollution controls when a car is undergoing testing, and off when it is back on the road, allowing it to spew out harmful levels of nitrogen oxide.

Volkswagen has subsequently revealed that beyond the nitrogen oxide scam, it had also understated carbon dioxide emissions, including in petrol cars.

The carmaker -- whose divisions include Audi, SEAT and Skoda as well as its truck and commercial vehicles -- now faces the sizeable task of recalling 8.5 million vehicles throughout Europe.

Volkswagen car sales fell 5.3 percent in October as the pollution cheating storm hit European demand.

Deliveries slipped 1.3 percent in western Europe compared to a year ago, with weakening demand seen in Germany, Spain and Italy.

Global sales were however lifted by its biggest market China, where deliveries rose 1.8 percent to 233,500 cars for the month.