Naseby ultramarathon record holder Marty Lukes will go into this year's 160km race as the firm favorite.
Lukes and 49 other runners entered in the 160km race will set off on the first of 16 10km loops near Naseby at noon today.
If Lukes runs anything close to the record he set in 2013 (15hr 30min), he will finish about 3.30am tomorrow.
The Christchurch runner, who also set the event's 100km record (8hr 21min 6sec) in 2011, set the 160km record the year the distance was introduced.
He did not compete last year, when Dunedin's John Bayne won the race in 16hr 48min 24sec.
Bayne, who represented New Zealand at the world 24 hour championships in Italy in April, will not compete this year, after his ''training went out the window'' due to a lung infection he picked up in London, and the flooding of his South Dunedin business.
However, Glen Sutton, who finished second a year ago, has entered the race less than a month after finishing 49th out of 100 runners in the gruelling Badwater 135 in California.
Sutton completed the 160km race in 18hr 53min 46sec last year, but will probably have to do significantly better to threaten Lukes.
Heather Barnes, who was the fourth woman across the line in 23hr 23min 50sec a year ago, is back for another crack at the longest distance in the event, and has a real chance of a podium finish in a small women's field.
Twenty runners have entered the 100km, 24 the 80km, 35 the 50km and 18 the 60km teams race.
The 10km loop runners will become accustomed with starts in Wet Gully Rd, about 1km from Ranfurly Naseby Rd.
Half of the loop is along a gravel road, while the other half is on a forest track beside the water race, which was built for gold mining in the 1860s.
The 80km and 100km races start tomorrow at 6am, while the 50km and 60km team races start tomorrow at 10am.
