It's billed as "the world's coldest and toughest ultra" race — and few would argue, after this year.

The long-distance, backcountry Yukon Arctic Ultra race, which began Thursday in Whitehorse, was put on hold on Friday after a slew of competitors fell victim to hypothermia and frostbite, calling for help, and dropping out of the race.

"We are in what we refer to as 'high alert status,'" says a notice on the race website.

The temperature in Whitehorse as racers set off on Thursday morning was hovering around –30 C. Overnight, it was closer to –45 C, race officials say.

"We were hoping most of them will get through the night without major problems. Unfortunately, this was not the case," the race website says.

As of Friday afternoon, several competitors had already been retrieved from the trail, and some have gone to hospital to be treated for frostbite.

Around 50 people started the long distance race in Whitehorse on Thursday. Many would drop out after the first bone-chilling night. (Philippe Morin/CBC)

'Rescue me!'

Mark Kelly, a Whitehorse photographer, found himself unexpectedly busy on Friday morning, picking up racers in distress on his snowmobile and delivering them to safety.

He had arranged to meet one of the racers on the trail, freelance journalist Eva Holland, to take some photographs for her. He didn't get far out of town before he was sidetracked.

"I was maybe five or eight kilometres on the trail, and a fellow hopped out of the bush and waved me down and just said, 'rescue me!'. Poor guy, I really felt for him. He was definitely hypothermic," Kelly said.

Kelly gave the cold man some hot tea, loaded him on his sled, and took him back to his truck to warm up and wait to be picked up. Kelly then set off again to meet Holland.

Again, he was stopped before he reached her. Another man was in trouble, and calling for help.

"After the second fellow with the blackening fingers, I thought, this is serious," Kelly said.

"One of the fellows, he'd stopped [to camp] because he was freezing cold, but his hands were so frostbitten that he couldn't even open his Thermarest. So he was laying, literally, right on the frozen ground — no wonder he was hypothermic."

Kelly eventually made it to Holland, who in the meantime had also called for help. Her fingers were frostbitten, but she was in good spirits, Kelly said.

"She said, 'sometimes the story is better when you don't make it through.'"

He brought Holland back to town, where she planned to go to the hospital to get checked out.

And a photo of me from late yesterday afternoon, maybe ~20 miles into the race? <a href="https://t.co/RrJKBH9TUT">pic.twitter.com/RrJKBH9TUT</a> —@evaholland

More cold nights ahead

It wasn't clear on Friday whether, or when, the race might resume. Race officials say it depends on the weather.

The forecast is not promising — According to Environment Canada, temperatures were again expected to approach –40 C overnight on Friday, and could stay consistently around –30 in the coming days.

Any racers who haven't dropped out, and manage to reach the Dog Grave Lake checkpoint, will have to stay there. Race officials says there's a wall tent set up there, with space for everybody.

"It won't be comfortable, but will sure be warmer than outside," the race website says.