Detectives are hunting the armed offenders who fled the BP petrol station at Bellata, near Narrabri, on the Newell Highway in a car at speed.

The men were armed with a broken bottle and fuel and entered the store about 4.20am, threatening the store attendant.

Oxley Detective Acting Inspector Jason Darcy said the pair then splashed fuel on the victim's face.

"The fuel was splashed on the employee's face and upper body," he said.

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"The pair then made serious threats and demanded cash."

The victim handed over a sum of cash and the men fled, taking off at high-speed, headed south on the Newell Highway towards Narrabri.

"Police are appealing for anyone travelling on the Newell Highway about 4.30am on Monday, who might have seen a car travelling at high speeds, or who might have dashcam footage," Detective Darcy said.

"We believe there were a number of trucks that were travelling on the highway at that time between Narrabri and Bellata, and we're just appealing for any motorists who might have seen anything.

"Similarly, anyone that might live along that stretch that has CCTV, we would urge anyone with information to come forward."

The victim was not physically injured, but was shaken by the incident.

"This was a serious incident, an armed robbery involving serious threats, so we would urge anyone with information, or anyone who might have been driving past and who saw the men or their car, to come forward," Detective Darcy said.

Anyone who can help detectives is urged to contact Oxley police on 6768 2999.