The errant sheep who appeared wearing a mammoth fleece began undergoing a risky shearing operation from 9am in the hope of saving its life.

The RSPCA estimates the sheep - who has been dubbed Chris, by the person who found it - has "five years of wool on him" and it "could barely walk".

Shearer Ian Elkins took about 45 minutes to finish the first pass and estimated that the 47cm fleece weighed about 40kg - and it came off in one piece.  It will be officially weighed at midday.

A New Zealand sheep - known as Shrek - that had avoided musterers for six years found fame in 2004 when it was discovered in a cave with 27 kilograms of unshorn wool. But the Guiness World Record belongs to another New Zealand sheep, Big Ben, with 28.9 kilograms of wool shorn off in January, 2014. 

Mr Elkins said smashing the record was a "bit of a buzz" but a challenge.

"Just the sheer volume and actually getting into the fleece was quite a challenge," he said. 

"There was five of us [shearing the sheep] - everyone held a leg or a shoulder."

After the sheep was mildly sedated, Mr Elkins and his team rolled the animal on to its back and sheared it in two layers, beginning with the belly.

"We had two cut it in a couple of layers because the weight of the fleece was pulling on the skin - to minimise the cuts," he said. 

"The fleece will have no commercial value. It's not a great quality of fleece, there's quite a bit of matter from running around in the bush all those years. It appears it has never been shorn before and its probably about six years old."

RSPCA ACT spokeswoman Jane Gregor said she was surprised by the sheep's calmness and condition. 

"The sheep itself actually started walking towards the shearing equipment. I think it was going, 'Get this thing off me'," she said.

"Considering how stressed the sheep was yesterday after being captured we were worried about this and we were expecting it to take two to three hours.

"It was quite relaxed through the whole process. We only had to stop on one occasion just to check heart rate but everything was fine."

Ms Gregor said the sheep was undertaking a vet exam Thursday morning but it appeared to be healthy.

"We're just tidying him up and finding a nice coat to keep him warm," she said.

"We were quite surprised, carrying that around you wouldn't expect him to be eating terribly well. He's not flyblown anywhere. He's one very lucky sheep."

She said the organisation had no idea what it was going to do with the fleece, but Chris will likely be offered for adoption in a week or two.

The sheep was found by a member of the public near Mulligan's Flat and rescued by a team of five from the local RSPCA and was being sheared by a shearer, his son and three helpers.

The team put out an urgent call for a shearer and its fame quickly spread. Apparently the RSPCA even had media requests from Polish news about the woolly animal.

It is believed the sheep had not been near humans for several years. And RSPCA ACT boss Tammy Ven Dange initially warned the process of shearing could lead to shock and death.

However, she said it needed to be shorn as soon as possible as Merinos were bred for the specific purpose of growing wool, and leaving it as it was would be cruel. The sheep was lightly sedated during the process to give it the best possible chance of survival.

"There could be infections, flystrike, [the coat] could prevent him from going to the bathroom. There could be a really nasty thing under that coat but we won't know that until we get there," she said.

with Alexandra Back