The Bungendore Trans Tasman Sheepdog Trial continues on Friday, Saturday and Sunday.
Spokeswoman Kylie Victory says there are 126 entries in the top three categories.
A handler and a dog attempt to get three sheep through obstacles and into a pen within 15 minutes, losing points along the way.
"It's an amazing display of how a person and a dog can work together,'' Kylie said.
The action is at the Bungendore Showground in Matthews Lane Bungendore from 7.30am to 5pm.
"Basically until we can't see the sheep anymore,'' Kylie said, with a laugh.
A canteen is also available with homemade food, drinks and tea and coffee.