You are not permitted to download, save or email this image. Visit image gallery to purchase the image.
Greene, who has competed internationally in long-distance, 24-hour events, will be using the shorter distance as speed work.
She finished second in the 50km race last year in 2hr 40min.
Her main opposition will come from Bridget Dickson, Jo Dowling and Haley van Leeuwen.
Nick Beekuis, who was third in the event last year, will start as favourite in the 52km men's mountain bike race. He was timed at 2hr 33min 25sec last year but the track will be slower this year after the October rains.
2Beekuis could be challenged by veterans Chris Henderson and Geoff Keogh, who have entered in the masters men's grade but will start at the same time.
Dunedin policewoman Mel Aitken is the favourite in the women's 21km run. The main challenge could come from Letty Walmsley, who was seventh last year.
The 12km run for both men and women will likely be dominated by New Zealand track and field representative Rebekah Greene, who is entered in the junior women's grade.
She competed at the world junior track and field championships in Barcelona this year and holds the Otago senior women's 1500m and 3000m records.
The Coastal Classic started with 138 mountain bikers. Running and walking events have been added.
Race director Wayne Jopson expects 500 competitors to start tomorrow. There are six events being held: Craypot run (12km), Akatore Creek run (21km), Moturata views walk (12km), mountain bike experience (15km), Coastal Classic mountain bike (women's) and Skyline course (52km).
All events start and finish at Livingstonia Park at Taieri Mouth. The action begins at 10am.