Police in Italy said on Thursday they had arrested 12 people allegedly involved in a ring that transported migrants from Tunisia to Sicily, with six suspects still unaccounted for. 

The suspects, 11 Tunisians and seven Italians, allegedly used small boats with powerful engines to transport between 10 to 30 migrants at a time from various towns on the Tunisian coast to Sicily off Italy.

The journey took under four hours, police said in a statement.

The migrants were "subjected to inhumane and degrading treatment", and the trip put their lives in "serious danger", police said.

The ring was run by a Tunisian man and woman from the Sicilian town of Niscemi - despite both being under house arrest at the time.

They relied on the help of a series of other people tasked with logistics such as money collection and putting up newly-arrived migrants.

The crossing, paid for in cash in Tunisia before departure, cost between €3,000 and €5,000 per person, meaning the alleged traffickers were pocketing between €30,000 and €70,000 per trip, police said.