Italian police have arrested more than 160 alleged members of the 'Ndrangheta mafia in what has been hailed as a historic setback for the group behind much of Europe's cocaine trade.

More than 40 arrests were made on Wednesday in Calabria, the secretive crime group's southern homeland.

The bulk of the arrests came in dawn raids in towns and cities across the much wealthier north of Italy, where the group has spread its tentacles in recent years in order to launder huge drugs profits.

A total of 117 people were arrested in the region of Emilia Romagna including six alleged bosses of a semi-autonomous clan that has spent the last 20 years infiltrating one of Italy's richest and most productive areas, Bologna's chief prosecutor Roberto Alfonso told a press conference in the region's capital.

Franco Roberti, the national anti-mafia prosecutor, hailed the operation which led to Wednesday's arrests as "historic and unprecedented".

"It is an impressive and decisive step against the mafia in the north. This is a deeply implanted and very dangerous criminal organisation," he said.

The 'Ndrangheta is considered the most powerful crime syndicate in Italy, thanks to its role as the principal importer and wholesaler of cocaine produced in Latin America and smuggled into Europe via north Africa and southern Italy.

That trade is worth billions and previous police operations have indicated that the 'Ndrangheta has well-established links with Colombian producer cartels, Mexican crime gangs and mafia families in New York and other parts of North America.

Wednesday's arrests were the latest in a series of high-profile operations which have confirmed the hitherto little-known expansion of 'Ndrangheta across Italy from Calabria, the underdeveloped "toe" of the boot-shaped country.