Runners in this year's Ironman Australia triathlon at Port Macquarie got a surprise as they made their way through the challenging final leg on the New South Wales Mid North Coast.

A male koala, known to inhabit the area, made its way straight across the course in front of runners and towards a gum tree.

The moment was captured on camera by local resident Jason Hannah, who lives near the triathlon course.

He said the koala, which he calls Big Boy, was familiar to him.

"He lives behind our place, so we see him every day, he goes over there every couple of days and sits in the gum trees on the riverside," he said.

"Everybody leaves him alone, they let him do his own thing … he's one of the residents, really."

Mr Hannah posted a video of the koala on social media and said he received thousands of responses.

Cheyne Flanagan, an advisor with Koala Conservation Australia, said she had seen the video and the koala appeared to be in good health.

"It looked to me to be a young male and looked to be in excellent condition, which was great to see," she said.

"It was on a mission, heading straight across the road to a forest red gum on the riverbank.

Koalas face habitat loss pressure

Ms Flanagan said while it was encouraging to see a healthy male koala, it reflected the struggles koalas faced in urban areas.

In August last year, a koala was spotted walking along a beach just south of Port Macquarie and that raised similar concerns.

"Urban koalas and ones in rural areas are not doing so well, they are continuing to decline at an alarming rate.

"The number of koalas being hit by cars recently has been concerning … it's also the rise in disease and disease tends to get manifested in areas where habitat has been disturbed."

Ms Flanagan said the NSW government, under the NSW Koala Strategy, was trying to restore as much habitat as possible.

"People can also play a part, by slowing down when driving in known koala areas, and calling wildlife carers if they see an injured animal," she said.