Preheat oven to 500°.
Remove giblets and neck from duckling; reserve for another use. Rinse duck under cold water; pat dry. Trim excess fat. Starting at neck cavity, loosen skin from breast and drumsticks by inserting fingers, and gently pushing your hand between the skin and meat.
Combine five-spice powder and 1 teaspoon salt. Sprinkle spice mixture under loosened skin; rub into the body cavity. Tie ends of legs together with cord. Lift wing tips up and over back; tuck under duckling.
Spread rock salt in bottom of a shallow roasting pan. Place the duckling, breast side up, on rock salt. Pierce skin several times with a meat fork. Insert a meat thermometer in- to meaty part of thigh, making sure not to touch bone. Bake at 500° for 45 minutes or until the thermometer reaches 180°. Cover duckling loosely with foil; let stand 10 minutes. Discard skin before serving. Garnish with fresh herbs, if desired.