Human remains have been found in the search for a couple missing in northern New South Wales after a bushfire which started more than a month ago due to a lightning strike.

Authorities had been looking for a 77-year-old man and 68-year-old woman missing from Coongbar, 70km southwest of Casino in Australia, news.com.au reports.

"Police yesterday attended a location at Deadmans Creek in Coongbar in relation to concerns for residents," NSW Police Superintendent Toby Lindsay said.

"Unfortunately, a short time ago, two human remains have been identified."

Advertisement

He said the coroner has been advised of the deaths as a result of the Long Gully bushfire, which has been considered "not suspicious" for a considerable period of time.

"We have no further information in regards to the families. To a wider extent the families have certainly been apprised and close family liaison has occurred today," Lindsay said.

"I can confirm a 77-year-old male and a 68-year-old female are believed to be the people that have died at this premises."

NSW Rural Fire Service Commissioner Shane Fitzsimmons described it as a tragic end to the search.

"It's a horrible outcome," he said.

Fitzsimmons said the Long Gully fire had been burning for many weeks near Drake but flared up again on Tuesday and spread across the Clarence River, impacting the rural areas of Ewingar and Coongbar.

Fire investigators have determined it began as the result of a lightning strike on September 5.

Fitzsimmons said the couple's bodies were found inside a "significantly damaged" home and confirmed no other people remained unaccounted for.

Advertisement

"You're talking about a remote, relatively isolated place that's been heavily impacted by fire," he said.

Earlier, NSW RFS Inspector Ben Shepherd said authorities "started off with around about a dozen people that were unaccounted for".

Richmond Valley mayor Robert Mustow told ABC the loss of a local timber mill would hurt 30 employees and have a "big impact on our community".

The Brisbane-to-Sydney rail line has been cut and won't be operational again for an estimated five days, the mayor added.

NSW Transport Minister Andrew Constance tweeted that stretches of the rail line had been damaged and the Rappville rail bridge destroyed.

It's believed the fire that ripped through the small village of Rappville on Tuesday afternoon may have been deliberately lit with NSW Emergency Services Minister David Elliott labelling the potential arson a "bastard act".

Fitzsimmons says in the absence of any other obvious cause the blaze is being treated as suspicious.

"We've got to call it out — it's a heinous crime, a criminal act," he told Nine.

Lindsay this afternoon said all fires were treated with suspicion until proven othwerwise.

Strikeforce Cleander has been formed to investigate the cause of the fire.

The Busbys Flat and Drake fires, which joined together in recent days, have burned 115,000 hectares. At least 29 homes, two community facilities and 72 outbuildings have been destroyed, with more damage expected to found.

Fitzsimmons said 34 bushfires continue to burn across NSW, eight of which remain out of control.

However, all fires are currently at the lower "advice" alert level after a number of emergency warnings were downgraded on Wednesday.

Allan Robertson lost his Rappville home and was left with the clothes he was wearing, his phone and "my worst thongs".

He said he was uninsured and his partner was in palliative care. "It was just like a massive fireball. There was nothing you could do. The heat was horrendous," he told Ten yesterday.

The NSW RFS said a number of residents were treated for minor burns and breathing difficulties.

Prime Minister Scott Morrison today said the Federal Government will provide "whatever assistance is necessary".

The fire service says residents likely won't be able to return home for a number of days given trees are down across roads and powerlines are on the ground. The fire service also warned that even though better conditions were forecast today, blazes could flare again.