The Moonee Valley Racing Club has unveiled an international bonus attached to the Cox Plate, with the winners of selected top-level overseas races eligible for an even bigger pay-day should they win Australasia's weight-for-age showpiece.

The MVRC outlined some of the details on Tuesday of the Cox Plate International Bonus sponsored by Ladbrokes.

The club said over the coming months it would partner with a number of leading middle-distance weight-for-age Group One turf races around the world, the winner of which would be eligible for a $A2 million bonus should they also win the $5 million Cox Plate at The Valley in October.

The first race to be included is the JRA Group One Takarazuka Kinen (2200m) on June 23 in Japan, with additional races to be announced in the coming weeks.

First prize money for the Cox Plate (2040m) is $3 million, not including the international bonus.

"The MVRC continues to promote the W.S. Cox Plate around the world as we look to attract the best middle-distance turf horses to The Valley to contest our great race," MVRC chairman Don Casboult said.

"This year we celebrate the 99th running of the W.S. Cox Plate and we look forward to crowning a new champion following the record-breaking achievements of (four-time winner) Winx."