Officials told ANSA the blaze was believed to be arson.
The fire broke out Monday afternoon, and by Tuesday it stretched over a half-mile from Monte Canino to Conca del Re. Officials are worried the park's famous Loricate pines will be all but consumed by the flames.
The park chief said the strategy for fighting the blaze was to be a "360-degree attack, with numerous hotbeds and primers organized scientifically, in addition to a favorable wind."
ANSA reported arson is typically thought to be the cause of most forest fires in Italy.