Fireball-like flames and thick black smoke were seen near the Bologna airport. Traffic was blocked in the area, and videos and photos from the scene showed burned-out vehicles and a partially-collapsed roadway.
He said he thought the tanker had probably been carrying liquid petroleum gas. "I thought it was an attack".
The explosion occurred near Borgo Paginale to west of the city, very close to Bologna airport, at around 2:00 pm (1200 GMT), the Italian fire service said on Twitter.
Police closed off the road where the crash took place as well as the surrounding area of Borgo Panigale, on the outskirts of the city of Bologna.
Bologna is the lively, historic capital of the Emilia-Romagna region, in northern Italy.
Italian news agencies have reported that multiple injuries were caused by flying glass from broken windows. Aerial photos showed a gaping hole left in the raised highway.
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According to the MailOnline, officers have said the blast could be felt in the busy terminal and was caused by an accident on the nearby motorway.
"I was in the house and I heard a huge bang and screams from the window". "There was panic in the neighborhood, because it wasn't clear what happened".
Firefighters are now battling the flames at the scene on the bypass in Borgo Panigale, according to local reports.
The accident was similar to one on Saturday, when a truck laden with tomatoes crashed into a white van and four migrants died.
Italian police posted a video showing the damage down to the bridge after the blast, showing a crater in the road.