The Rural Fire Service (RFS) says an immense bushfire in the Snowy Monaro region of NSW is being controlled after destroying properties yesterday.

The properties lost were all in the Bumbalong area, between Bredbo and Michelago.

The fire was downgraded to advice level on Sunday morning.

It is not yet known how many properties were lost.

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Dangerously high temperatures were a catalyst for aggressive fire behaviour on Saturday and some blazes combined to create their own weather systems.

Around noon a spot fire from the huge Orroral Valley bushfire in the ACT jumped into NSW and sparked the Clear Range fire.

The Orroral Valley fire was accidentally ignited by a military helicopter this week and has ignited several fires nearby.

The RFS was using 16 water bombing aircraft across the Clear Range and Orroral Valley fires.

Further south in the Bega Valley, a cluster of fires generated pyro-convective columns with lightning.

How pyro-cumulonimbus clouds form over firegrounds. ( Supplied: BOM )

The Postmans Trail fire and Big Jack Mountain fire are now at Watch and Act.

"[The weather systems] are obviously dangerous and create increased hazards and volatility," Commissioner Fitzsimmons said.

Firefighters were issued with safety alerts and told to seek refuge when appropriate.

The Border Fire, just north of the Victorian border, which has been burning for weeks also flared up on Saturday but eased by the late evening.

There is a cluster of fires in the Bega Valley, three at emergency level. ( Supplied: RFS )

The RFS has warned people to stay off the roads and protect themselves from the heat of the fires at home.

"We are no way near the end," RFS public liaison officer Aaron Howard said.

Bega Shire Council operations manager Ian Campbell said the surrounding communities had been preparing on Saturday and evacuated early.

"There's around 120 people at the Bega evacuation centre and around 25 people at the Bermagui surf club now," he said.

"But most people are with friends and family."

The Erskine Creek fire threatened Leura and Wentworth Falls earlier this month. ( Twitter: RFS )

The Erskine Creek fire in the Blue Mountains also grew in size on Saturday afternoon but was not close to any properties.

The blaze has been burning for several weeks in the catchment to the north of Warragamba Dam and south of Bullaburra.