Training has been stymied by the unusually long hot summer which saw August and September set 40-year record temperarture highs.

Organizers Oxfam Hong Kong have had to reset the date of the race three times as a result.

The 100km trek from Sai Kung to Yuen Long, mostly over the challenging MacLehose trail, begins on Friday morning at Pak Tam Chung in Sai Kung and ends on Sunday when all teams will have crossed the finish line at Po Leung Kuk Jockey Club Tai Tong Holiday Camp in Yuen Long.

Forecasters predict 14-20 degrees Celsius temperatures.

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Eric LaHaie, 29, coordinator of the S36 team who are sponsored by Columbia stores and Racing the Planet online stores, said: "I suspect this year more people will finish in the cooler weather."

LaHaie, 29, a manager at Racing the Planet, said his team aimed to finish in 14 hours.

KPMG partner Rupert Chamberlain, 39, a veteran of 12 Trailwalkers, said: "It is a difficult course. I have practiced it three times and it is certainly a much tougher finish than before. It is a very heavy finish as opposed to a flat finish. But realistically we are shooting for a top 10."

Clement Dumont, 32, a research professor at the University of Hong Kong's Swire Institute of Marine Science, has done both the Mont-Blanc race and the desert endurance race Marathon des Sables.

Dumont said of Trailwalker: "You go up and down so you are not always in very good shape, and because you are a team it's not up and down at the same time for everybody. So I think this is the challenging part in running as a team."