Firefighters are working to access trapped rural communities that have been cut off after a bushfire "blew up" near the Victorian border.
As many as 30 people may be isolated in the small village of Wonboyn on the NSW south coast after the 52,000-hectare Border Fire tore through the region.
"There's a search and rescue operation for those who may still be trapped in townships such as Wonboyn," RFS spokesman Ben Shepherd told the ABC on Sunday afternoon.
"Indications are (that) there were at least 20 to 30 people who were at the Rural Fire Service shed at Wonboyn. We are working to get access to them."
Bega-based RFS liaison Greg Potts said Wonboyn residents had sheltered successfully inside the shed and firefighters were now planning how to get supplies to them.
"Wonboyn and north Wonboyn came under direct attack. The residents there - 20 remain sheltered successfully in the RFS shed.
"We are working with those communities to look at all sorts of arrangements to get fresh food and provisions into them, probably by sea."
The RFS said those sheltering in Eden should leave north if that was their plan.
"If you are in Eden and surrounds and your plan is to leave, and you are not prepared, leave now toward Merimbula or Pambula."
Bega Valley Shire Council spokesman Ian Campbell said the region was living under "horrible" skies turned orange by the fires.
"These terrible skies extend from the north of our shire to the south of our shire. They are truly horrible skies to live under."
Mr Potts said the border fire, which was still burning at an emergency level on Sunday afternoon, "blew up" on Saturday night when a southerly wind change swept through.
"We saw extraordinary fire behaviour last night," he said.
"The fire basically created its own weather and ran at an extraordinary speed from the NSW border."
Mr Potts said there was "no margin for safety" as crews battled the blaze.
"At one stage the border fire was moving at 6km/h. The lack of visibility is making aerial reconnaissance impossible."
NSW RFS Commissioner Shane Fitzsimmons said "lots of people" had evacuated the town of Eden as the fire approached on Saturday night.
"It's moving a bit further north and towards rural and isolated property just to the west of Eden," he told reporters on Sunday morning.
"It's still pretty active down there, and there is lots of attention from local firefighters."
Containment efforts were hampered overnight after firefighters lost power at an important water pump.
"In a disappointing development, we have lost power to the pump at Ben Boyd Dam and the Kiah borefields," the Bega Valley Shire Council said at 3am on Sunday.
"We are working to supply water from Pambula to Eden - this will be at a much reduced volume however.
"If you are still in Eden, only use water for personal safety purposes so the firefighters, who are doing such an outstanding job, have water."