Within minutes of the explosion, several videos emerged on social media showing the moment the billowing smoke erupted into a fireball.
Police said in a statement that between 60 and 70 people were injured, some with serious burns.
Fire raging on the motorway outside Bologna
- via Getty Images Firefighters work at the scene where the tanker truck exploded.
The explosion occurred near Borgo Paginale to west of the city, very close to Bologna airport, at around 2.00 pm (12pm GMT), the Italian fire service said on Twitter.
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The city's airport is around 3.7 miles north-west of the city centre in northern Italy's Emilia-Romagna region. Video captured by a witness shows the explosion and a plume of smoke filling the sky. Aerial photos showed a gaping hole in the highway next to the tanker.
Firefighters have since put out the blaze, a spokesman said, adding that efforts were under way to ascertain the cause of the explosion and the precise number of victims.
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Casualties in the explosion have yet to be reported.
Some people were reportedly hit by flying glass as windows shattered in nearby buildings. The interchange connects two major highways linking northern Italy with the Adriatic coast, a popular destination as Italy heads into its major summer holiday next week.
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