The New South Wales Rural Fire Service raised alert levels for the Dunns Road, East Ournie Creek and Green Valley bushfires about 8.30pm on Friday.

At 9am Saturday, all fires were burning at 'advice' level.

The Hume Highway near Gundagai was closed about 10pm on Friday night because of the proximity of the Dunns Road fire, which was burning at emergency. It has since been reopened.

Firefighters were on high alert amid concerns that Friday's dangerous conditions could cause massive blazes to Canberra's south-west to spread deep into the Brindabellas and come close to the Monaro Highway north of Cooma.

The New South Wales Rural Fire Service warned that Friday's searing heat, with temperatures reaching into the high 30s and low 40s and across southern NSW, followed by gusty south-westerly change, "will make fire behaviour erratic and dangerous".

RFS spokesperson Angela Burford said the service had "well over" 2000 firefighters fighting 134 fires statewide, and most of those were deployed in the Snowy Mountains and South Coast fire grounds.

A total fire ban was in place across the ACT and surrounding areas for Friday.

Prime Minster Scott Morrison has urged "everybody to get yourself to a place of safety, listen to instructions and stay together and support each other as you have been doing so well over so many months now, particularly the last few weeks".

Speaking on ABC Radio's AM show, Mr Morrison shrugged off the sustained criticism of his handling of the bushfire crisis, saying that "copping flack goes with the job".

Firefighters are particularly concerned about the huge Dunns Road fire, which is burning on multiple fronts and has so far burnt through more than 313,000 hectares, and blazes burning to the north of Adaminaby, all of which are out of control.

Ms Burford said fire danger in the area would peak between 5pm and 8pm as a cool change passed through the area, bringing with it strong and unpredictable winds.

Among the firefighters working to contain the Adaminaby Complex fires on Friday was former prime minister Tony Abbott.

Capt Simon King in charge of the RFS in Adaminaby said of Mr Abbott: "He's just a firefighter doing hard work with his North Beach Strike Team. He's doing the hard yards. Mr Abbott is just an ordinary crew member."

In the ACT, firefighters were quick to extinguish a grass fire that broke out at Nicklin Crescent in Fadden just before 8am on Friday, and a few hours later brought a grass fire that had ignited near Woodcock Drive in Gordon under control.

ACT Emergency Services Agency Commissioner Georgeina Whelan said fire crews had been deployed at strategic location across the ACT on Friday to ensure a rapid response to any outbreaks, and firefighters had also been dispatched to support RFS firefighters battling the blazes around Adaminaby and the Brindabellas.

The temperature in Canberra is forecast to reach 39 degrees around 5pm before a cool change moves through between 8pm and 10pm.

Ms Burford said the arrival of the cool front would be a period of particularly high risk because of the unpredictable and erratic winds associated with it.

The RFS has advised those living in the Brindabella and Goobragandra Valley areas, particularly south of Argalong and west of Brindabella Valley Road to leave early.

"Do not be in the path of this fire," the fire authority said.

Those living south of Tumbarumba and west of the Kosciuszko National Park have been issued similar warnings.

The RFS said fire danger in the Scabby Range Nature Reserve area will be extreme Friday, with the potential for fires burning in the area to behave erratically.

On the South Coast, firefighters warn that fires including the huge Currowan blaze, the Charleys Forest fire could spread west, while there is a chance the Clyde Mountain fire could spread south and potentially link up with the Badja Forest Road blaze.

Ms Burford said RFS crews were working to slow and contain these blazes but strong and erratic winds blowing along the coast and through the ranges just inland would make conditions dangerous throughout the day.

It has warned those living in areas of potential fire spread that their communities may come under threat from embers or fire fronts.

"If your plan is to leave or you are not prepared, you should not be in this area on Friday," the RFS said. "Move to a large town outside this area, or if you are on the South Coast, move to an area that has already been burnt or go to the beach. Stay away from the red areas."

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Bureau of Meteorology forecaster Andrea Peace said that a cooler change due to sweep across areas of southern NSW late today will lower temperatures but associated gusty south-westerly winds with speeds of at least 80 kilometres per hour in places, will inflame the fire risk.

Ms Peace said the change would bring little rain.

"There may be some showers around the southern districts but no significant rainfall," she said.

But Ms Peace said more settled and humid conditions should prevail on Saturday and Sunday.

Canberra's air quality has vastly improved in the past 48 hours and ACT monitoring stations rated air quality on Friday morning as good or very good, with the index of dangerous 2.5 micron particulate matter between 27 and 33 points - well below the 200 point level considered hazardous.

The clearer air has enabled Questacon to reopen on Friday after being closed the previous two days.

The venue said its staff had been working hard in the past two days to clear air within the building and announced that bushfire-affected families would be able to visit free of charge through to the end of the month.