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.
When used by Hiruzen in the anime, he merely spews out a single stream of fire which seemingly had no definitive shape. It would also seem that, by increasing the output of chakra to the flames, they become hotter and appear whitish in color.