The eight are suffering mild hypothermia and are under observation at Queenstown Lakes Hospital after being rescued from the Southern Lakes Ultra Marathon.
Seven were athletes and one was a race official.
The alert was raised when a personal locator beacon was activated at 1am this morning.
By early afternoon 10 personal locator beacons had been activated, the Rescue Coordination Centre said.
Rescue Coordination Centre Operations Manager Michael Clulow said at least 110 people associated with the event were in the area.
Race officials had told rescuers they had now accounted for all competitors and officials. Most were safe at the Macetown Camp area, he said.
There has been heavy rain in the area, causing the Arrow River to rise and the weather was forecast to remain inclement over the next 24 hours.
Fire and Emergency Queenstown Lakes assistant commander Nic McQuillan said Fenz had been notified this morning there may be around 100 people trapped at Macetown with the river flooding.
Ground crews flown in by helicopter had made contact with athletes.
"They confirmed that the racers that remaining - approximately 90 - are well and don't need rescuing. We are checking a couple of other huts in the area at the moment to make sure."
About 125 runners have signed on for this month’s event, about 60% from overseas — mainly from Australia but also the United Kingdom, United States, the Netherlands, Germany and Hong Kong.
The seven-day, six-stage race covers 261 kilometres with competitors tackling the first 35km stage yesterday.
Heavy rain has been falling in the area overnight and forecasters have issued a heavy rain watch for Otago with rainfall possibly reaching warning levels in some areas.
Race co-ordinator Emily Sutton confirmed several runners have been evacuated and were under observation.
Individual families would be contacted directly by organisers.
