A month before that, the curly-haired 10-year-old was named junior champion at the South Coast Zone athletics championships, coming first in sprints and the high jump.

But on Monday, Byron's life was cut short when a sand dune collapsed on him at Terrace Beach on the NSW south coast near Eden.

The Wyndham Public School student had been enjoying the first day of the school holidays, digging with his four-year-old brother.

When the small dune collapsed, Byron's brother ran to their mother, Lia, a trained nurse who tried to revive her boy.

Paramedics treated him at the scene but he died at Merimbula Airport, before he could be airlifted to Canberra Hospital on Monday.

"To me it sounds like he was digging head first into the sand dune and got carried away like a kid would, digging a little hole like a little cave," family friend Peter Guenthroth told Channel Nine.

"He was into exploring caves and doing all natural things."

Bega Valley Mayor Bill Taylor said the close-knit community would be reeling.

"In a village like that, everyone knows everyone," Cr Taylor said.

"We can only struggle to comprehend how family and friends are coping today. We can't even imagine what they are going through.

"It's every parent's nightmare that something like this might happen. A child doing something so innocent and the next minute you have a tragedy on your hands.

"We send our heartfelt sympathy to the family and friends."

Detective Superintendent Peter O'Brien described the accident as "a tragedy of immense proportions".

"They were just doing what all kids do on the beach, digging holes and mucking around," he said.

"Something that would be happening every day on every beach in Australia. This one, unfortunately, has turned into the tragedy we are talking about."