Concerns over rockfalls has forced Milford Mountain Classic organisers to shorten Saturday's race by 20km.
The course change will see the cycle race, being staged for the second time, start about 1km west of the Homer tunnel, rather than at Milford Sound and finish in Te Anau.
The New Zealand Transit Agency had made the call due to rockfall risk at the western entrance of the Homer Tunnel, a situation which has seen the road closed at night from the Hollyford turn-off to Milford Sound since early December.
NZTA Southland area manager Peter Robinson understood the move would disappoint some riders, but believes the right decision had been made.
''Cyclists would have limited ability to get to safety, even with the safety systems we have in place and that is a risk we are simply not prepared to take and while obviously disappointed, the race organisers understand our position.''
Race committee chairman Don McFarlane said the safety of the cyclists was paramount.
''Safety is the number one priority and if NZTA believe there is a real risk to participants, then there is no alternative but to move the start to avoid this hazard.
''We are delighted that the event can still go ahead, albeit as 100km instead of 120km, and believe the 100km route will still provide participants with a challenging race through some of the world's most spectacular scenery.''
Mr McFarlane said it was hoped the situation would have settled enough for the full event to return in 2014.
About 150 riders had entered to do the full race on Saturday and Mr McFarlane said a discount might be offered for any who chose to return for the 2014 race.
- © Fairfax NZ News
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