Firefighters work at the scene where a tanker truck exploded on a motorway just outside Bologna, northern Italy, on August 6, 2018 (Photo by - / AFP) (Photo credit should read -/AFP/Getty Images)

A tanker truck carrying flammable material exploded Monday on a highway overpass near the northern Italian city of Bologna, killing at least two people and injuring up to 70 as it partially collapsed the raised roadway, police said.

Some people were reportedly hit by flying glass as windows shattered in nearby buildings.

Italian police said between 60 and 70 people had been injured, some with severe burns, in the midday accident on a major highway north of the city.

Officials did not immediately know what kind of explosives were in the tanker, but the news agency ANSA said it was liquefied petroleum gas.

The explosion reportedly came after a traffic accident. Videos show flames shooting up in the air after the explosion, replaced later by a thick black cloud of smoke. Aerial photos showed a gaping hole in the raised highway next to the tanker.

Italian television Sky TG24 said the flames fell to the lower level, setting off secondary explosions in a car lot below. It said some of the injured had been hit by flying glass when windows in nearby buildings exploded.

Firefighters said the flames were extinguished some three hours after the explosion, and they were working to cool the area to facilitation operations, ANSA reported.

Authorities said a major highway interchange had been closed north of the city due to the accident. 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.