Todd Sligar, Mitchell Holloway and Ethan Hertslet were driving south along the Mitchell Highway north-west of Dubbo, when their ute veered off the road on Saturday morning.

The black 4WD ute wrapped around a tree near Trangie, killing the three men - aged 24, 21 and 17-years-old - at the scene.

A green P-plate sign was visible as emergency services from around the rural region descended on the crash scene just before 8am.

Remarkably, the three dogs that accompanied the boys on their pig hunting trip survived the crash and were treated by a local vet.

The absence of skid marks on the road has led police to believe the driver may have fallen asleep.

"[F]atigue is the most likely outcome there," NSW Police Highway Patrol Inspector Phil Brooks said.

The deaths have reverberated through the community in Orange, where all three men hail from.

"My life is a darker place today...so many things left unsaid...so many paths left to smooth out," Tosh Pintos wrote on Facebook.

"A few more beverages to be had...im breaking inside but have to stay strong."

His partner Tanika Pintos - believed to be Mr Sligar's sister - wrote: "I just want him back just to let him know I love him just one more time."

Narromine Shire mayor Bill McAnally said the stretch of highway had seen quite a few accidents in recent years and drivers had be very much aware of fatigue.

"I believe these were all young blokes on P-plates," he said.

"There would be some devastated parents this morning having lost three young men."

Mr Sligor's aunt, Jo-ann Yates, said he was a "beautiful boy" who loved to hunt.

"He was very caring, we're all suffering," she said.