It is being described as a bombshell for the French police.
Four senior officers – including the deputy police chief in the city of Lyon, Michel Neyret – are in custody, being questioned over drugs and corruption allegations.
Neyret has often been featured in the media as France’s “supercop” for his record on fighting crime.
Claims of international drug trafficking and money laundering are also being investigated.
David Metaxas, a lawyer in Lyon, said Neyret was being accused of links with organised crime, but he says for the police those links have always existed.
Neyret, whose wife is also in custody, is reportedly suspected of giving informants drugs seized by the police and helping them to resell it.
The French Interior Minister, Claude Guéant, said: “This would be very painful for the national police, painful to see one of their own leave the right path. If guilt is established, all appropriate sanctions will be taken.”
Swiss bank accounts are being probed and other alleged drug dealers are in custody. Another man arrested is said to be suspected of supplying the deputy chief with luxury cars during visits to the French Riviera.