The Wuuluman fire, between Wellington and Mudgee, was detected on Wednesday afternoon.

However because of the hilly terrain, the blaze proved difficult for firefighters to bring under control and it was only contained on Monday.

The RFS said it hasn’t identified the cause of the fire but is conducting an investigation with police into how the fire started and would also investigate how the vehicle came to be in the path of the fire.

A source told the Daily Liberal the fire was started by a person on a property in the Wuuluman region before it got out of control. It was not suggested it was arson.

RFS media liaison officer Matthew Apps said the RFS was also investigating how a category seven tanker, a four-year-old Isuzu, had been destroyed but said the greater focus was on controlling the fire.

“RFS fire investigators have come out to inspect the scene but the investigation is still in its early stages,” he said.

Mr Apps said there were different stories about how the tanker had come to be engulfed by flames and that would be a focal point of the investigation.

“Things the investigation will look at include where was the vehicle located at the time of the fire, where was the fire coming from, how many people were on the tanker and were they inside our outside the vehicle at the time,” he said.

“There are a number of people that have to be interviewed but they are involved in fighting the fire, which is the priority.”

RFS Orana team leader Superintendent Lyndon Wieland said he wouldn’t speculate on what had caused the fire. “We haven’t had time to begin the investigation. We are far too concerned about keeping the fire in a box. Until the enquiry takes place, we won’t really know what has happened,” he said.

A spokesperson for the Minister for Emergency Services David Elliott referred the Daily Liberal to the RFS and said Mr Elliott wouldn’t comment, but said he supported the RFS investigation.

Crews fighting the Wuuluman fire continued to strengthen containment lines and mop up on Tuesday. Teams from across NSW were being brought in to relieve local crews on Wednesday.