French prosecutors have opened a serious fraud investigation into Volkswagen over devices the German automaker fitted into cars to cheat in emissions tests, a judicial source told AFP on Tuesday.

VW, a former paragon of German industry, has been plunged into its deepest-ever crisis after acknowledging that it had installed emissions-cheating software into 11 million diesel engines worldwide.

The probe, launched by Paris investigators on February 19, concerns Volkswagen cars sold in France, the source said.