The explosion ripped through one of Italy’s biggest oil refineries in Sannazzaro de” Burgondi, near Pavia, about 25 miles south of Milan.
Emergency plans were activiated as residents were urged to stay in doors amid fears thousands of tonnes of fuel could go up in flames.
The Department of Civil Protection in the Province of Alessandria opened nearby emergency centers as they feared the worst.
The blast at the Eni refinery generated a fireball belching black smoke which could be seen for miles around.
There were no reports of casualties.
A statment from Eni said the company is working with firecrews to bring the blaze under control.
The spokesman added they are now investigating the cause of the explosion.