ACT Emergency Services Agency commissioner Georgeina Whelan said three bushfires burning out of control southwest of the ACT could cross the border over the weekend - if the "worst-case" scenario eventuated.

Commissioner Whelan said based on the agency's modelling, the Dunns Road, Adaminaby Complex and Atkinsons fires would not pose a threat to Canberra's residential suburbs on Friday. If that situation changed, Canberrans would be told immediately, she said.

On Thursday night the NSW Rural Fire Service released maps showing the southern tip of the ACT had the potential to be impacted by the Adaminaby Complex fire and ember attacks as the fire spread to the east.

A total fire ban has been declared for the ACT for Friday, with temperatures set to reach 40 degrees in the nation's capital. Northwesterly winds of up 35 km/h are predicted for the middle of the day, before west to southwesterly winds sweep through in the late evening.

On Thursday, local firefighters extinguished the small Hospital Hill fire which had been burning in the southern remote area of Namadgi National Park.

While Friday's extreme conditions heighten the risk for new fires to ignite within the ACT, the immediate priority for local firefighting crews will be helping their NSW counterparts in tackling blazes burning through the Snowy Mountains region.

Commissioner Whelan said ACT fire crews have been deployed to fight the Adaminaby Complex fire, which is about eight kilometres from the territory border. Local crews were also helping NSW Rural Fire Service with surveillance and reconnaissance around the Atkinsons and Mount Morgan fires, which are burning through Kosciuszko National Park.

All of the fires were burning at advice level on Thursday night.

Cooler conditions and patches of rain throughout this week have allowed fire crews, with the support of Defence personnel, to plan and build containment lines, including near the ACT's southwestern border. Water bombers have also been used in attempts to contain the blazes.

But commissioner Whelan said she couldn't guarantee the fires wouldn't spread and enter the ACT, noting that weather during this fire season had been "very unpredictable". Large fires were also capable of creating their own weather patterns which made their movement difficult to predict, she said.

"The Adaminaby fire is obviously a risk in entering the ACT, which is why we are undertaking the work that we are," she said.

"The Atkinsons fire to our west, if it takes a run in the next few days, that could also cross into the ACT border.

"Then of course we have the Dunns Road fire and the activity around Tumut. Depending on the weather patterns, and the level of containment done by NSW Rural Fire Service, that could also cross into our border."

Commissioner Whelan said if a fire did break out in the ACT, crews deployed to NSW could be called back at short notice.

"We would not put out anything that we could not withdraw straight away," she said.

"I will not leave the ACT exposed. Our community is concerned is about what is happening in NSW, so we are contributing to that [firefighting effort].

"Equally, they are concerned about what will happen in our borders, so we are balancing that out as well."

In anticipation of another spell of extreme weather in the ACT, Chief Minister Andrew Barr on Thursday declared the territory would remain in a "state of alert" for the "foreseeable future". The declaration puts Canberrans on notice to prepare for the possibility of a bushfire emergency.

"As we have said, on our worst bushfire day, we can't have firefighters protecting every single home," Mr Barr said.

"Again, we ask and stress that if you haven't downloaded your bushfire survival plan and filled it out, please do so now."

Temperatures in Canberra are expected to cool over the weekend, with the Bureau of Meteorology forecasting a top of 28 on Saturday and 24 on Sunday.