Alaskan musher Brent Sass, currently the leader in the 2016 Yukon Quest, was the first to arrive at Dawson City at 12:21 p.m. local time.

Canada Border Services officers are on hand to screen mushers as they arrive in Dawson after crossing into Yukon from Alaska. This is the first year that mushers haven't been pre-cleared to cross the border.

When Sass was asked if he had anything to declare, he replied "14 dogs."

Sass was first into Dawson for the third straight year, despite the fact his dogs were battling a stomach bug during the first half of the race.

Sass said it was a challenge keeping the dogs fed but they seem to have recovered.

"On the trail, other than what was coming out of their butts, they were really good," he said.

As the first musher to arrive at Dawson, Sass will win four ounces of gold if he completes the race.

Fellow veteran Quest musher Allen Moore arrived second at Dawson, about two hours after Sass. Hugh Neff, another veteran, arrived about 30 minutes after Moore. 

Yukon's Ed Hopkins is the fastest Canadian, currently in fifth place and expected to reach Dawson late Wednesday night.

The teams set off from Fairbanks, Alaska, on Saturday. Sass is running nearly six hours ahead of the projected race pace.

"We've had really good trail in Alaska this year so it allowed [mushers] to pick up some time there," said race marshal Doug Grilliot.

"And over the last three to five years, the dog teams have just gotten faster."

Doug Grilliot

Doug Grilliot, a Yukon Quest race marshal, says 'really good trail' in Alaska has teams travelling at a faster pace than expected. (Chris Windeyer/CBC)

Weather has also helped pick up the pace this year. It's been cool but not too cold, though Grilliot said the race could have used a bit more snow.

"The conditions have been as close to perfect as you can imagine."

Teams will take a mandatory 36-hour layover in Dawson City before beginning the second half of the 1,600 kilometre race to Whitehorse. 

For mushers it's a chance to sleep while team handlers care for the dogs. Race veterinarians also examine the dogs.

with files from Chris Windeyer