Fire ripped through a 20-storey residential building in Milan, northern Italy, leaving rescue workers scrambling to make sure no-one had been caught in the flames and thick smoke.

The blaze started on the upper floors of the tower on the southern outskirts of the capital of the Lombardy region.

"The flames then spread to the lower levels," causing thick smoke, the Italian fire services said on a Twitter account.

The building houses some 70 families, who were being contacted in an effort to make sure no-one was missing.

"We are sure that there was time to get out, but until the controls are finished we cannot be entirely sure," Mayor Giuseppe Sala told reporters at the scene.

"But we are optimistic because people had time to get out."

He said about 20 people were evacuated without incident.

Mr Sala said there were no reports of injuries or deaths, but that firefighters were kicking down doors, apartment by apartment, to make sure there were no victims.

A huge plume of black smoke rose from the reinforced concrete building named the Torre dei Moro and was visible for kilometres.

The 60-metre-tall building, part of a recent development project, was designed to look like the keel of a ship and included an aluminium sail on its roof, which burned and fell to the street in pieces. 

Flames continued to burn inside nearly three hours after a dozen fire trucks and ambulances responded to the alarm. 

Unidentified residents told the Corriere della Sera newspaper that the panels on the facade were supposed to have been fire-resistant.

Plans for the project said it had 16 residential floors plus two underground levels.

AFP/AP