The user kneads their chakra into flames, which are then manipulated into a genuine-looking dragon. Since the art of having the flames obey the user's will is outrageously difficult, its mastery is restricted to a limited number of skilful shinobi. The flames are divided to launch a left side, right side, and frontal assault in all three directions at once, turning the enemy into ash in a matter of seconds.
In the anime, when used by Hiruzen, this technique is depicted as a high-pressure stream of fire which has no definitive shape. It would also seem that, by increasing the output of chakra to the flames, they become hotter and appear whitish in colour.