A van carrying oxygen cylinders exploded in Milan on Thursday, destroying around a dozen cars but causing no injuries beyond light burns to the driver, officials said.

Television footage showed flames metres high and black smoke sweeping across the Porta Romana residential neighbourhood south-east of the Italian city's cathedral, Duomo.

Milan mayor Giuseppe Sala was quick to rule out a deliberate attack, telling reporters on the sidelines of an event: "It's a van carrying oxygen cylinders." 

Fire service officer Carlo Cardinali confirmed the vehicle had been carrying oxygen, saying the exact cause of the blast was still being investigated.

"At the moment, only the driver" had reported injuries, he told journalists at the scene, and he managed to escape with "light burns".

Another fire service spokesman earlier told AFP the person hurt had injuries to their arms and legs.

"I heard three big explosions and more that followed," Giuseppe, a 39-year-old labourer working on a site nearby, told AFP.

"I came straight away to see what was happening, and the whole street was on fire, people were running."

Footage published by the fire service suggested a powerful blast, showing what it said were about a dozen parked cars that had been completely burned out.

On the street between them, several canisters were visible next to the remains of a destroyed vehicle.

Buildings in the immediate vicinity were evacuated, including a school, while damage was reported to a nearby pharmacy and two apartments.