Several vehicles caught fire in the centre of Milan after an explosion.
Sky TG24 reported the blast came from a van, which has since been confirmed by the Italian city's mayor.
Italian daily paper La Repubblica said the vehicle was carrying oxygen cylinders when it exploded, triggering "domino explosions".
A number of other vehicles became engulfed in flames, and plumes of thick black smoke were seen rising above the wreckage.
At least five cars and four mopeds were alight, with the blaze scorching the facades of buildings on the street - including apartments and a pharmacy, according to the newspaper.
A nearby school and nursing home were evacuated.
The city's mayor, Giuseppe Sala, ruled out foul play and said the driver of the van had told the fire brigade the blaze had started in the engine.
"He quickly grabbed the oxygen cylinders he was carrying... he tried to limit the damage but then there was an explosion," the mayor said.
He added the van driver had suffered minor injuries.
Four people were injured in the incident, according to local media reports.
There were no reports of any deaths.
Firefighters put out the flames in the Porta Romana area of the city - which was cordoned off by police.
Footage and images on social media showed crowds spilling out onto neighbouring streets amid the rising smoke and commotion.