Emergency services have declared a total fire ban in the ACT as an out-of-control bushfire in Namadgi National Park reaches 2575 hectares in size and burns 9km south-west of Tharwa and 15km from the suburb of Banks.
The fire is at a watch and act warning level and travelling in a south-easterly direction towards Boboyan Road.
ACT Emergency Services Agency commissioner Georgeina Whelan said the fire was however spotting up to 5km east and south from the main fireline.
The ESA has advised that people in Tharwa and the remote area of Orroral Valley could be affected by a bushfire near Boboyan Road, Apollo Road and Top Naas Road.
Residents have been advised to activate their bushfire survival plan.
Residents in Banks, Calwell and Gordon have been advised to monitor the situation and stay up to date.
ESA will hold community meetings at the Tharwa Town Hall at 10am Tuesday and at the Community Centre at Uriarra at 6pm.
Emergency services said fire was burning near Link Road along the Smokers Trail inside the national park in Tennent.
Australian Defence Force and State Emergency Service personnel have started doorknocking, and residents who have been advised of the emerging situation will have their properties tagged for recognition.
Landholders on Boboyan Rd and Apollo Road have been contacted to make sure they are prepared for the fire.
Erindale College will be available as an evacuation centre if needed. EPIC has been opened as a horse evacuation centre.
At a 5.15pm briefing, Ms Whelan on Monday asked landholders in the area to activate their fire protection plans.
"Our priority is to contain the fire," she said.
Ms Whelan urged people in the area to stay up to date on the ESA's website, and via its social media channels.
She described the firefighting conditions over the next week of hot weather as "challenging".
"We have a tough seven to 10 days ahead of us."
However, the ESA commissioner said she was confident that emergency services personnel were "well capable of undertaking the operational tasks ahead of them."
Boboyan Road has been closed from Namadgi Visitor Centre and south from Shannons Flat. Access to the area is restricted to residents, local landholders, emergency services and Australian Defence Force personnel only.
"If you do not need to be in this area, for your safety, do not enter or return," Ms Whelan said.
ACT Chief Minister Andrew Barr said the fire was generating a lot of smoke, which was affecting Tharwa.
"We're encouraging these residents to stay indoors and keep up to date with the latest information from the ESA," he said.
Multiple fire crews are staging at various locations, with the Namadji Visitors Centre being used as a forward command post. Tharwa was also being set up as a secondary staging area but has not yet been activated.
Ms Whelan urged people not to be concerned if they see emergency service personnel their area.
"They are either doing a reconnaissance or they are forward posted to support an early response in support of the community in order to keep you safe," she said.
Nineteen firefighting units are trying to contain the fire that started in the Orroral Valley about 1.50pm on Monday.
Eleven helicopters and large air tankers are conducting waterbombing and aerial surveillance.
Ms Whelan said the cause of the fire would be investigated.
Late on Monday afternoon the NSW Rural Fire Service was pulling its crews off the Cotter Hut Rd as the fire began to impact that area.
Local property owner and RFS Southern Districts Brigade member Steve Angus was on his way back from the NSW South Coast late on Monday afternoon.
The RFS had sent heavy plant to his property and he said he had been getting updates on the fire from his brigade members.
"We're pretty well prepared for it if it comes," he said.
"The house is well-protected, the cattle are OK, and there's not much grass to burn."
A tanker was sent to the Namadgi Visitors Centre along with two dozers. Waterbombing efforts are being carried out.
The Corin Forest recreation area will be closed until further notice due to the fire and the buildings are being protected by fire sprays.
Emergency services closed a number of areas around Namadgi, including walking areas, Ms Whelan said.
She said those areas were clear of any bushwalkers.
The ESA has been told a family member collected a bushwalker reported to be in the area earlier on Monday.
Tuesday's forecast is for winds becoming westerly 20 to 30 km/h in the morning then shifting east to southeasterly in the evening.
The temperature is expected to reach 35 degrees.
NSW has declared a total fire ban for Tuesday, for Yass Valley, Queanbeyan-Palerang, Southern Ranges, Goulburn Mulwaree and Upper Lachlan.
The total fire ban in the ACT is in effect until midnight Friday.