This week's devastating fire at Tarago that destroyed a home and burnt out almost 3,400 hectares was sparked when a bird flew too close to powerlines, according to the NSW Rural Fire Service (RFS).

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The blaze, referred to by firefighters as the Currandooley fire, is still burning in the vicinity of Taylors Road, Bungendore Road and Mount Fairy Road, but is now under control.

On Tuesday, it tore through a property near Bungendore in matter of minutes, gutting a house and destroying several cars and livestock.

RFS inspector Andrew Gray said it was likely the bird flew too close to high-voltage powerlines, causing them to arc, which resulted in the bird catching alight, which then set nearby dry grass on fire.

He said the bird's carcass, "rumoured" to be a crow, was found by investigators.

Bird causing fires has happened before

Mr Gray said the cause was uncommon but unavoidable.

"It's not commonplace, but it has happened. There's been reports of birds throughout NSW creating fires," he said.

"Unfortunately this one happened on a very bad day.

"It's just an act of nature."

Rain hindering vehicle access to affected areas

Despite showers across the region this morning, firefighters from NSW and the ACT remain at the fire ground and are still working to extinguish the blaze completely.

Inspector Andrew Gray (left) says rain is hindering access to the fire site. ( ABC News: Jesse Dorsett )

Mr Gray said the rain had helped contain the fire, but it was causing new issues.

"It's helping us to maintain the fire where it is at, but it is hindering us with our access to the ground … [as it] has made the ground soft," he said.

"Now it is turning from dust to mud."

The alert level for the fire is set to advice and the fire danger rating for the NSW southern ranges fire area is still set to high.

A spokeswoman for the NSW RFS said it was unlikely the fire would be extinguished today.