The fire was upgraded about 2.30pm on Friday due to embers spotting to the north of the blaze near Butmaroo. It had been at an advice level for most of Friday.
"This morning,with the variable winds,we started seeing quite sporadic wind and fire activities and started spreading in all directions,"said NSW Rural Fire Service spokeswoman Angela Burford.
"It took a significant run to the east after westerly winds."
She said there were some open-grass areas with minimal fuel and parts where the fire was self-extinguishing,but other parts which were prone to quick burning,and winds causing spot fires.
"Even this evening,we've seen spot fires start kilometres in front of the fire front,"she said.
An emergency warning was sent to areas west of Braidwood,and then a second one to seek shelter to the the town.
"It's probably within a couple of kilometres of the town now,"Ms Burford said.