CCTV footage then shows the men bending down and using an instrument to unbolt the 80-100kg statue from the concrete plinth.
"I watched the artist [install] it and it was very securely fastened," he said.
Gow said they're then seen rocking the gnome side to side, eventually wriggling it free.
They left the scene about 12.45am on Christmas Day, and putting the statue into a vehicle parked outside the Gallery's Kitchener St entrance.
Gow said he hoped that the statue was currently sitting in someone's backyard as it would be near worthless doing anything else with it.
"I'm hoping that they have put it in someone's backyard and it's sitting there as a keepsake otherwise they'll be looking to melt the bronze down which would be a bizarre thing to do. In reality, the bronze is worth, maybe, $2000. Whereas the sculpture itself is a $55,000 object.
"I'm sure any scrap metal dealer, meeting someone turning up with something like that, will be scratching their head and asking a few questions."
It was unclear what vehicle was used but CCTV had captured a "very clear picture of a Caucasian male's face".
"They were mostly wearing hoodies but there was this one point where they weren't and our security camera which is trained on the sculpture picked up his face."
Staff first discovered the statue was stolen on Saturday after a horrified director Gary Langsford drove past, noticing it missing.
"I came straight in and could see that the work had been removed forcibly, through the chips around the edge of the concrete where the bolts went through and realised that we had a problem.
"And then when I reviewed the security footage sure enough there it was. I couldn't believe it."
He said he phoned artist, Kregar, to tell him the news. He initially thought he was joking, unfortunately he wasn't.
The gnome had been welcomed by the community in its short time; it had even been adorned with a santa hat.
"People noticed it, people stood there and had their photo taken with it and it put smiles on people's faces so for someone to come along and do this it's just robbing the public of an experience they otherwise could have."
He now urged for the thieves to return the art work and for members of the public who walked past the men as they stole the structure to get in touch with police.
"You can see a group of people going past wearing Christmas hats, there was cars going past and various pedestrians ... anyone who saw anything we'd love to hear. But really, to the people who have stolen it, it's an art work, it's precious and we want it back so they can call us or email us or we can come and get it."
The Gallery had exhibited works on the plinth for the past 20 years.
He believed the thieves likely knew they would be closed for a couple of weeks from Christmas Eve.
Gow said this was the first time there had been any incident. In future they would review what was put outside on display and ensure it could only be moved by a hiab and truck.
