Police patrolling Bucketts Way at Tugrabakh, about two hours north of Newcastle, arrived at 3am at the scene where an SUV had slid down an embankment.
They found a 45-year-old man and an 11-year-old girl dead in the vehicle.
Two boys, aged eight and nine were freed and taken to hospital with non-life-threatening injuries after being trapped in the vehicle for some time.
NSW Police Chief Inspector Timothy Bayly said the passengers and driver were all known to each other.
Police had earlier received reports of concern for the welfare of the man and the children, with officers told they might have been travelling to a relative's home.
An investigation was launched when they failed to arrive at the property.
A man and a child have died in a crash on the Mid North Coast overnight.— NSW Police Force (@nswpolice) MORE INFORMATION ➡https://t.co/zrxmqWlQmwOctober 18, 2024
"The original call was made about 1am … we don't know what time the accident actually occurred," Chief Insp Bayly said.
The vehicle was allegedly involved in an earlier minor crash and police have called for witnesses to both events.
Bucketts Way is a 151-kilometre single-lane rural road that links Gloucester to Taree.
Police are investigating the circumstances of the crash and a report will be prepared for the coroner.
Three men have also died in Western Australia after a vehicle crashed into an unoccupied home in Carlisle, in Perth's east, about 5am on Saturday.
The men, one aged 34 and two aged 22, were passengers in the vehicle and died at the scene.
Two other male passengers, aged 19 and 23, were hospitalised with serious injuries, WA Police said.
The 22-year-old driver received minor injuries. He remains in police custody and is assisting officers.
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