Seth Marsden rips it up in front of a crowd of 20,000

Imagine racing around a track, flying over jumps and kicking up dust on your motorbike, all while a crowd of 20,000 roars in your ears.

That is what awaits eight year old Bungendore resident Seth Marsden on Saturday night when he competes in the Australian KTM Supercross Challenge in Sydney.

Seth will compete alongside 19 other seven and eight year-olds in the first race of its kind held in Australia.

He said he is pretty happy to be selected.

"It's, like, once-in-a-lifetime."

And while Seth gets a bit nervous when racing, he also feels excited.

"I love riding- you can do big jumps, you can go fast, you can do tricks sometimes, and you can do it with your mates."

Seth was selected for the competition based on his academic results at St Gregory's Primary School in Queanbeyan, as well as his record in over a year of racing.

He was introduced to riding by his dad, firefighter Ken Marsden.

"(Seth) asked to go racing at the end of 2015 and we've been going pretty full-on from then," he said.

"He's at the point where he's riding faster and faster, and jumping bigger and bigger jumps."

Mr Marsden said that he doesn't really worry when his son is racing, because training at facilities like the Moss Institute Training Facility in Nerriga, NSW has made him competent on the track.

"Because he's got the coaching and he knows how to ride correctly, it takes the uneasiness away."

The full competition experience on Saturday includes practice sessions on the track, an exhibition race and the opportunity to watch the entire event and meet VIPs.

"(Seth) will meet tons of his heroes and idols, it'll be amazing," Mr Marsden said.