Wellington's Round the Bays has been cancelled for the first time in 22 years, with Omicron modelling ruling out the option of postponement.
The event's organisers issued an update earlier this week saying the community run would not go ahead as scheduled on February 20, due to New Zealand's move into the red traffic light setting.
They signalled a decision would be made by the end of the week, but this morning posted an update saying postponement was not an option.
Phil Gibbons, the chief executive of Nuku Ora, the organisation that delivers the event, said it was tough to have to cancel such an "iconic" event in the Wellington calendar.
He believed it was the first time the event had been cancelled in its 45-year history, but certainly in the 22 years Nuku Ora had been running the event.
While they had considered postponing to April 3, Gibbons said they had looked into the modelling of Omicron in the community.
"It was kind of a bit of a smash at the end of March and early April," he said.
"The modelling around Omicron and its impact in the community was telling us that end of March early April will be when it's at its peak."
"Ultimately that's going to have a significant impact on our workforce and their ability to deliver but also on the participants and their ability to go out and enjoy themselves, and also on our huge volunteer workforce."
While they had only initially guaranteed a 25 per cent refund to race participants, Gibbons said they would be increasing this to 75 per cent, with the help of government support.
"We're hoping though that people will consider, given the nature of this event, perhaps donating that to one of the four charities that this event supports by way of funding."
The increase in refund would be made possible by the introduction of the Government's Events Transition Support Payment scheme, which Gibbons said they would be applying for.
"The reality is though that we need to look after our participants and refund them now," he said.
"We've taken a bit of a gamble there but we think it's the right thing to do in supporting our event and its participants."
Refunds would begin to be processed on Monday, and would take several weeks due to the volume of entries.
The community run around the capital's waterfront has been going for 45 years. Participants can enter categories including a half marathon, 5.6km buggy walk, and a 6.5km fun run/walk.
Gibbons said they were looking to deliver a virtual event, to reward paid participants who had trained for the race.
"We're looking forward to be able to deliver a virtual event some time in the near future, where people can still get out there, run their selected distance, perhaps create a competition among their workmates or their friends."
More details would be listed on their website and social media channels next week, he said.