Sala said the driver of the van had told the fire brigade that the blaze had started in his 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 that the driver had sustained only light injuries.
Firefighters quickly extinguished the blaze, which had sent clouds of thick black smoke into the sky.
Eyewitnesses said the fire appeared to have spread to a nearby building, which was evacuated. A local school was also evacuated.
