The accident took place around 2 p.m. local time in Borgo Panigale, an area on Bologna's outskirts, Italian newspaper Il Fatto Quotidiano reported.
A lorry carrying cars collided on a bridge with another tanker lorry containing highly flammable propane or butane.
Firefighters are now battling the flames at the scene on the bypass in Borgo Panigale.
Video on social media showed the tanker bursting into a very big mushroom cloud of orange flames and a thick plume of black smoke pouring into the sky.
A tanker truck explosion that caused a huge ball of fire has killed at least two and injured up to 70 people in Italian city of Bologna.
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Italian police told the ANSA news agency on August 6 that 14 people were seriously injured in the explosion, which was caused by a vehicle carrying flammable materials.
A huge explosion has rocked a motorway near an airport in northern Italy - killing one and leaving 55 people seriously injured.. Aerial photos showed a gaping hole in the highway next to the tanker.
Firefighters said the flames were extinguished several hours after the explosion, ANSA reported.
The blast triggered a series of explosions that grew in ferocity this afternoon.
Police said the explosion came after an accident at midday on a busy eight-lane highway near Bologna.