Dangerous fire conditions are building in NSW after temperatures soared across the state and strong winds fan erratic bushfire behaviour.
Bureau of Meteorology spokesman Grahame Reader says dangerous bushfire conditions spiked on Friday with hot temperatures reaching the mid 40s in the western parts of the state.
"We have another dangerous fire weather day unfolding, presenting a difficult combination of very high temperatures and changing winds," he told reporters.
"The northwesterly winds will be very hot."
Strong northwesterly winds with gusts of 60km/h have been recorded in parts of the state and are forecast to move up the coast of NSW, he added.
Authorities are also concerned about a strong southwesterly wind change with gusts of up to 90km/h which is expected to come through later in the evening.
"We are expecting a very significant, strong and gusty southwesterly change to come through, which has obviously got an abrupt shift in the winds, which is problematic in its own right," Mr Reader said.
"The change is critical. The winds really peak around the change and the directions shift is very sharp and particularly gusty."
The change is expected in Bega about 8pm, Nowra about 11pm and Sydney early on Saturday morning.
An extreme fire warning is in place for the southern slopes while severe fire warnings have been issued for the Monaro Alpine region, ACT, southern ranges and eastern Riverina.
The NSW Rural Fire Service said the southerly change would fan "erratic and dangerous" fire behaviour.
"We'll see hot temperatures, high 30s and low 40s, across parts of NSW. It's the hot, dry winds that will prove once again to be the real challenge," RFS Commissioner Shane Fitzsimmons told reporters on Friday.
Fire conditions will gradually ease early on Saturday as temperatures drop in the wake of the southerly change, Mr Reader said.
"There will be showers and isolated thunderstorms in coastal parts and adjacent ranges.
"These are probably not significant falls. There could be heavier falls locally but that won't be widespread."
Australian Associated Press