Two men were hospitalised and in life-threatening condition, one with burns on 55 percent of his body, local health authorities told the AGI news agency.

Fabio Balzani, head of the sports centre, said if the fire had occurred just a bit later, it could have been disastrous.

Some 60 children had been expected at the summer camp, and around 120 people booked to use the swimming pool as relief from a heatwave that has baked the city for the past week.

“It would have been a massacre, a catastrophe,” Balzani told AFP.

Andrea Quattrocchi, the local chief of the Carabinieri police force, also said the timely intervention of his team was crucial.

“They extracted a person alive from a burning car,” who was taken to hospital, he told reporters.

Witnesses said an ambulance exploded in the fire.

Ennio Aquilino, regional director of the Lazio fire department, said the petrol station explosion was caused by a “BLEVE” — a boiling liquid expanding vapor explosion—of the liquefied natural gas.

A BLEVE is caused by the rapid vaporisation of a pressurised liquid, normally when the vessel containing it is ruptured in some way.

“The effect is as if a bomb has gone off,” Aquilino told reporters.

Prime Minister Giorgia Meloni offered her sympathy to the injured and praised first responders for their quick work that helped avoid “this tragic event from having even more serious consequences.”