For a cost of 10,000 euros (about $14,000), Chinese emigrants were given a valid visa and work contract. Upon arrival in Germany, they were forced to surrender their passports.

'They stood in downright debt servitude,' Federau said.

The immigrant Chinese were given jobs, and those who were not trained chefs were quickly brought up to speed, investigators found.

The chefs were made to work for 80 to 90 hours a week, at an hourly wage of three euros ($4.26). Their lack of German language skills made it difficult for the immigrants to complain.

As for the people smugglers in Germany and their associates in China, the investigations revealed that they had pocketed 'revenues in the millions', according to Federau.