Reuters Italian media said a truck carrying cars collided on a bridge with another tanker truck containing inflammable materials.
He said he thought the tanker had probably been carrying liquid petroleum gas.
The video shows how a tanker truck moving on the road, but do not have time to brake in time and behind the trucks.
The accident caused part of the raised expressway to collapse.
At least 70 people are also injured. It collided with the vehicle before 2 p.m. local time (8 a.m. ET), setting off a fiery explosion and blasting a crater in the road, according to police.
People living far from the site of the explosion said the deafening blast shook their homes.
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Two people have been killed and at least 60 injured, Italian outlet La Stampa reports. Video and photos from witnesses showed a massive fireball shooting into the air on a highway in the suburbs of Bologna on Tuesday afternoon.
Others were injured by pieces of flying debris and glass the explosion caused in the surrounding area.
Italian police posted a video showing the damage down to the bridge after the blast, showing a crater in the road. The interchange connects two highways linking northern Italy with the Adriatic coast.
Italian firefighters tweeted that they've sent multiple rescue and emergency squads, including one from their urban search and rescue team.
Sky News reported that it took three hours for the flames to be fully extinguished.