A new dipping sauce is being promoted at McDonald's in Japan. A Willy Wonka-style contest where the lucky winner will receive an 18-karat gold McNugget.

Reportedly worth about US$1,500, competition entrants will have to follow clues on Twitter and around Japan to find the campaign's mascot, a mysterious thief called Kaito Nuggets, and the bejewelled nugget itself inside a five-piece McNugget pack.

"He may appear in some of McDonald's restaurants through the country, may throw out a ceremonial first pitch for a professional baseball game, or pay a visit to a prefectural governor making a surprising request entertaining people," the company said in a statement.

Twenty-one runners-up will receive a gift of a five piece pack of nuggets alongside the two new sauces, "Creamy Cheddar Cheese" and "Fruits Curry Sauce".