The model, who has not been named, was assaulted, drugged, handcuffed and stuck in a travel bag, police said in a statement.
A 30-year-old Polish national who resides in the United Kingdom was arrested on kidnapping charges. Lukasz Herba was arrested July 17 outside the British consulate in Milan while accompanying the woman, said Lorenzo Bucossi, the head of the Milan Police Mobile Command unit.
It was not immediately clear why the suspect took the model to the consulate.
Authorities said they are searching for at least one more person in connection with the kidnapping.
Taken to remote home
The model arrived in Milan on July 10 and already had a photo shoot booked through her agent for the following day, according to the police account.
When she walked into the apartment where the photo shoot was supposed to take place, two men attacked her, police said.
She was loaded into the trunk of a car and taken to a cabin on the outskirts of Lemie, a remote town in the Italian Alps, she told authorities.
The woman was kept handcuffed to a wooden chest of drawers in a bedroom for a week, police said.
According to the Italian police, the suspect used encrypted accounts to ask the model's agent for $300,000 to stop the online auction from going ahead.
He also allegedly told the agent that he was operating on behalf of "the Black Death group," an organization involved in illegal trafficking on the dark web, a layer of the Internet accessible only through anonymizing networks like Tor.
Italian investigators have since established that the suspected kidnapper had already organized several online auctions for the sale of abducted girls, referring to them as "prey."
The websites for the auctions included a description of the victim and a starting price but police said it was still unclear whether the suspect had made them up.
Investigations under way
Investigations in the case are ongoing in Italy, Poland and the United Kingdom.
The British Foreign Office said only that it is providing consular support to a British woman in Milan and that it is in touch with local authorities.
The Foreign Office declined to provide additional information on the woman, her condition and whether she is back in the United Kingdom.