The smugglers had the migrants pose as “unsuspecting Asian citizens, well-dressed, with little luggage, travelling in powerful and expensive cars, driven by Chinese citizens who had lived in Italy for years and spoke Italian”, police said in a statement on Wednesday.

Investigators were alerted to a possible ring after a Chinese citizen was stopped at the border between Italy and Slovenia in April during routine checks, and found to be transporting four undocumented Chinese.

A probe uncovered “the existence of a consistent, continuous flow of irregular Chinese citizens who, in small groups, were flown to the external European borders in countries (mainly Serbia) where they entered with a visa exemption”, the statement said.

“And then, from there, they were accompanied by car, through Bosnia, Croatia and Slovenia, up to the Italian state border”, it said.

Smuggled migrants were transported to a safehouse near Venice, where they stayed for one or two days before being taken on either to areas of Italy or other European Union countries like France and Spain.

The traffickers confiscated their passports at the safehouse and “from then on… (they) were exposed to severe exploitation until the debt incurred for the journey had been repaid”, the statement said.

The migrants were kept “without any possibility of a free or semi-free life, without medical assistance, with nothing except a bed and a place to work indefinitely,” police said, describing it as a sort of “slavery”.

Police arrested nine alleged members of the trafficking network during the operation and identified 77 undocumented migrants, “many of them women and some minors aged between 15 and 18”.