A 26-year-old Australian cyclist died in his sleep on Tuesday while participating in the eight day, 723km Absa Cape Epic mountain bike race.

James Williamson, who edited the Australian Enduro mountain bike magazine, was declared dead at 6.47am in the Ceres Private Hospital, where he was taken when his riding partner Shaun Lewis, 28, could not wake him, the organisers said in a statement.

Describing Williamson as a "strong young athlete", the race organisers said he had an uneventful ride on Tuesday and had felt "completely well with no complaints" at the end of the stage.

"He and his partner ate well last night and everyone who spent the afternoon and evening with him said that he was perfectly fine. After the first two stages they were in 18th overall position."

Williamson won the World Solo 24 hour mountain bike Championships in Canmore, Canada in 2008.

"After yesterday's [Monday's] stage two through singletrack paradise, he was all smiles, repeatedly expressing how he enjoyed yesterday's route. He will be deeply missed in the mountain biking media fraternity," said the race's international media director Sonja Guldner-Hamel.

"Wow, what a day," Williamson wrote in a blog about stage one of the Epic, which started on Sunday, on his blogsite jameswilliamson.com.au.

"The start saw us hit up a cobbled climb through a winery before a brief flat section and then yet more climbing, and more, and more ? then we were in some awesome singletrack before a long steady climb up to water point one.

"In between sucking up the pain in my legs as I clung to Shaun's wheel, I was able to take in the scenery below as we wound our way up the valley. It was sensational and riding in a bunch of guys from all over the world, a new experience for me.

"From there it was a hairy tarmac descent and into water point two for the biggest climb of the day. This was a tough one. Shaun set a solid tempo on the front and I did my best to keep up. This was the hardest point of the race for me and I was beginning to wonder what I was getting myself into.

"But soon enough we were into some rocky double-track and I felt a little better again. It was a long stage though. At about the 110km mark, over four-and-a-half hours in, we hit a seven kilometre section of rough railway track with sharp rocks and railway sleepers every half-metre.

"Our bikes bounced around as we grimaced our way through it and hoped it'd be over soon. It wasn't, it dragged out like nothing else and was damn tough, seeing the smooth road after that hellish section was pure bliss.

"So we got through that one and were able to enjoy a short downhill before the finish. What a massive day: 117km and a shade over five hours on the bike, bring on day two."

No prior complaints

When Lewis was unable to rouse Williamson for stage three at 5.10am on Tuesday, he phoned his media hospitality contact, who immediately notified the race doctor, Basil Bonner, of Medi-Clinic, the organisers said.

"Dr Bonner was at the site four minutes after he had received the emergency call. At that time bystander [Cardio Pulmonary Resuscitation] was already conducted. The medical staff conducted CPR for 1.5 hours, one hour on site and 30 minutes in the ambulance and in Ceres Private Hospital, where the patient was taken."

The organisers said Williamson had received no medical treatment during the race itself and beforehand, submitted the compulsory medical questionnaire which all participants had to have signed by a doctor.

"His medical form stated no previous medical condition of note."

News of Williamson's death had been conveyed by Bonner to his aunt Megan Patey and uncle John Lascellis, who would arrive in South Africa with his father on Wednesday night.

It had yet to be determined whether a forensic post-mortem would be conducted in South Africa or Australia.

Trauma counselling was being arranged for Lewis.

Absa Cape Epic race director Kevin Vermaak expressed condolences to Williamson's family, his partner Nicky and Lewis.

"James was a very enthusiastic mountain bike journalist who had expressed interest to ride the race over the last few years. 2010 was the year that he could fit it into his publishing schedule and he was thrilled to finally be participating in the race," said Guldner-Hamel.

This year 1200 riders from 50 countries are participating in the entirely off-road race, which started in Diemersfontein in the Western Cape and finishes at Lourensford Estate in Somerset West.

During this year's race, the 600 two-person teams are required to climb 14,635 vertical metres on their bikes.

Medi-Clinic staff were keeping a record of every single consultation by all participants either on the course or in the race hospital, the organisers said.

It said the medical staff included six race doctors, 11 paramedics, six nurses and four administration and logistics support staff, and 25 emergency care practitioner marshals with three 4x4 ambulances, five medically equipped all terrain vehicles, four response vehicles and a medi-vac helicopter on permanent standby.