Crews from Murrurundi and Quirindi responded to a call about 10.40pm to assist with a broken down locomotive stuck in Ardglen tunnel, which links the Hunter Valley and the state's northern interior.

The 488-metre tunnel is known for its narrow profile and steep approaching grades.

"The concern was that you start up a diesel locomotive and it's going to produce carbon monoxide," a Fire and Rescue NSW spokesman told Topics on Tuesday.

"They were concerned that there would be high levels of carbon monoxide in the tunnel and the driver would be in danger.

"We were called as a hazmat incident to go in there with our gas monitoring equipment and assess the air.

"Crews entered the tunnel wearing air-sets and with the gas detection [equipment]. Initially there was carbon monoxide still in the tunnel and it was deemed unsafe."

Quirindi senior firefighter Daniel Peterson told Topics engines on two locomotives remained running when the breakdown occurred, raising air quality concerns.

The train's drivers had walked out of the tunnel before the fire crews arrived.

After devising a plan and obtaining clearances, firefighters and a driver, who was provided with breathing apparatus, returned to the train and backed it out of the tunnel.

"Once we took the driver back in on safe air, he was able to start one of the front engines up and they released the brakes and rolled it back down the hill out of the tunnel," Mr Peterson said.

"Then we could do some atmospheric monitoring in the cabs, and get them clear, before the drivers could go back in and try and get it going again."

Mr Peterson said the job was "probably a first" for the upper Hunter crews. "It was a bit of a new thing for everybody," he said.

It's becoming quite common for local Fire and Rescue NSW crews to post photos of the jobs they're tasked to on social media.

The Quirindi crew uploaded a photo of what appears to be its firefighters inside the tunnel looking at the light at its end.

However the photo, taken by firefighter Sabrina McNamara, was actually taken from outside the tunnel with the locomotive's lights illuminating towards the crew.

The Ardglen tunnel is the oldest single-line tunnel in use in NSW and has long been the subject of potential deviations.

Proposals for a longer tunnel under the Liverpool Range have been put forward at various times over the past few decades.

An upgrade was once considered one of the region's most important infrastructure priorities but never eventuated.

Majority of the traffic that passes through the tunnel is coal trains travelling between the Gunnedah Basin and Newcastle's port.

Merewether artist Mitch Revs will paint a one-off art piece during Surfest this week to be raffled for a local Autism charity.

Doyle Partners, a firm of accountants and the naming rights sponsors of Surfest's Women's Pro, have commissioned the Novocastrian to paint a Surfest and Merewether beach-inspired artwork that will be used to raise funds for Surfing the Spectrum.

The local charity is a not-for-profit surf therapy initiative working to impact the lives of families and their children with Autism by providing learn to surf events.

The events promote ocean awareness, social inclusion and water safety.

Revs' artwork is first prize in the raffle, second prize is a Shortie twin-fin surfboard and third prize is a Surfest rash-vest signed by competing surfers.

Surfing the Spectrum director Tahlia Anderson said the charity heavily relies on fundraising and the raffle would be a significant boost to its ongoing programs.

"We're so lucky Doyle Partners thought of us, we're super, super grateful," she said.

Tickets are on sale in the Surfest precinct at Merewether beach all this week. The raffle will be drawn on Sunday.

Surfing the Spectrum is hosting its next Newcastle event at Nobby's beach on Saturday, April 18. Registrations for participants opens three weeks prior to the event, but volunteers can register on the charity's website - surfingthespectrum.org - now.