At about 1.15pm, Fire and Rescue NSW crews from Narrabri were called to the scene on the Old Gunnedah Road where they found two people trapped in one of the vehicles.

Ambulance and NSW Police were also on scene.

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Narrabri Fire and Rescue station commander Shane Bradford said crews quickly initiated a side-door extraction to free the pair and "allow paramedics to work on him".

"The male occupant driving with the other female was trapped by confinement," he said.

"The road was blocked north and south for 40 mins by police and the oil and debris were recovered by FRNSW and rendered safe and the three patients were taken to Narrabri Hospital."

Narrabri police officer Ben Stride said police are investigating whether the man had a medical episode, and veered into oncoming traffic.

"He's veered from his lane gradually over about 70m-100m, with one wheel missing, onto the oncoming traffic and hit the other vehicle. We believe his car was going somewhere between 40-50km/h," he said.

"The car he hit was travelling at 40km/h and tried to veer off the road to avoid the collision.

"Even though both cars were travelling at a slow speed it was still a big hit because neither braked."

Officer Stride said the man didn't recall the incident whatsoever.

"Because he's had some sort of medical episode he can't report the speed. We believe he had a bit of a bump on his head and doesn't recall the incident at all," he told the NVI.

Investigations are continuing.