The race begins at 6am today at Northburn Station near Cromwell.
The top endurance race is the 100miler, in which participants battle their way through a high-altitude race, which they have 48 hours to complete.
Race director Terry Davis said the best would finish the 100miler in 24 hours.
The course will have competitors climbing and descending around 10,000 metres.
Competitors would not be running for the entire race but would not stop moving - sleep was not an option, Davis said.
There will be three major races today - the 100miler and 100km and 50km races - and three fun races - 5km and 10km late-night races starting at 8.30pm and a 2km children's endurance race starting at 1pm.
A marathon was due to start at 6am today and a half-marathon starts at 1pm tomorrow.
Davis called the 100miler a "world of pain".
"Suffering is the prize and everyone's a winner," Davis said.
"It's not a running race, it's a mountain mission."
Close to 200 competitors from all over the world would be competing, Davis said.