Police confirmed late on Monday that three men had died and a five-year-old boy had been left with a broken arm following a crash at a property in Gundy, near Scone.

Emergency services were called to the property on Waverley Road about 5pm when the car was found by a neighbouring landowner.

It is believed the car drove off a cliff and rolled down an embankment. All four people on board were ejected from the car, police said.

It is understood the boy's father and grandfather were killed in the crash, along with Scone real estate agent Adam O’Regan. 

The men were believed to be inspecting the remote property on Monday morning.

Police said concerns were raised for the men's welfare on Monday afternoon when they failed to return from the trip.

Police and neighbours on quad bikes returned to the property on Tuesday morning, where investigations are still underway.

Glen Ramplin, an air crewman for the Hunter Region Westpac Rescue Helicopter, told Fairfax Media on Monday two helicopters were dispatched to the accident – one from Newcastle and one from Tamworth.

"The first call that the aircraft from Newcastle got was [Tamworth] had been called to a property up there for a car that had gone off a cliff," Mr Ramplin said.

The Tamworth medics arrived at the crash site first, about 6pm, and called off the second crew when they realised the boy was the only survivor.

Ambulance crews had to use quad bikes to get to the scene, he said.

Mr Ramplin said the boy was flown to Scone Hospital, where he was transferred in an ambulance to Newcastle's John Hunter Children's Hospital.

He remained in the hospital in a stable condition on Monday night.

Police began to examine the scene on Monday and will resume their investigation on Tuesday morning.

It is not yet known what caused the crash.

A report will be prepared for the Coroner.

- with Georgina Mitchell