Numerous people missing in New South Wales bushfires, authorities say it could be arson

A number of residents are still missing in northern NSW after a bushfire, which police believe was deliberately lit, destroyed more than a dozen homes in the Rappville area.

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

Superintendent Toby Lindsay won't say exactly how many people are still unaccounted for.

"We are worried about a number of people," Mr Lindsey told reporters today in Rappville where at least 11 homes were lost.

"We always hope for the best but we've obviously got to treat it at its worst. We've seen the devastation in town. It's a very large fire and it's still active."

Richmond Valley mayor Robert Mustow asked locals to report into authorities.

"We have still got some people missing and the longer that goes on the more concerning it gets," Mr Mustow said.

"I would ask people, if you've vacated your property, please go down to the evacuation centre (and) register," the mayor told ABC TV.

Mr Mustow said 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.

NSW Rural Fire Service commissioner Shane 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 the Nine Network.

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

NSW Police district commander Superintendent Toby Lindsay has said the strike force "will leave no stone unturned so we can provide answers for the rural communities impacted by this disaster".

Teams are still assessing how many properties have been lost or damaged in the suspicious blaze which is believed to have started in the Busbys Flat area on Friday night.

Across the Busbys Flat and Drake fires - which have joined together in recent days and burned 115,000 hectares - at least 21 homes have been destroyed. Fifteen were in the Rappville area while the remainder were impacted by the Drake blaze.

Mr 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 yesterday.

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 Network Ten yesterday.

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

Prime Minister Scott Morrison said today the federal government will provide "whatever assistance is necessary".

The RFS says residents likely won't be able to return home for a number of days given trees are down across roads and power lines are on the ground.

The fire service also warned that even though better conditions are forecast for today, blazes could flare again.

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Dozens of other fires continue to burn, says 1 NEWS Australia correspondent Ryan Boswell. Source: 1 NEWS