The Orroral Valley fire burning in Namadgi National Park has been upgraded to emergency warning.
There was no threat to properties in Tharwa or Canberra suburbs, as of 2pm.
The fire, which started on Monday afternoon in the Orroral Valley, has burnt almost 3000 hecatres.
As of 1.30pm on Tuesday, the fire was nine kilometres south-west of Tharwa Village and 15 kilometres from suburban areas in Tuggeranong such as Banks.
The ACT Emergency Services Agency said the fire was approaching the areas of Boboyan Road, Apollo Road and Top Naas Road.
"Leave the affected area immediately. If you are not in the area, do not return," it said in a statement.
"Leaving immediately is the safest option. Soon it will be too dangerous to drive.
"If you are in the areas of Boboyan Road the safest route is south towards Shannons Flat.
"If you are in the areas of Apollo Road and Top Naas Road the safest route is north towards Tharwa along Naas Road.
"This route has been cleared and is being monitored by emergency services for people evacuating.
"An evacuation centre has been opened at Erindale College.
The Bureau of Meteorology has warned heatwave conditions forecast for later in the week could increase the fire danger.
Earlier, ACT Emergency Services Agency commissioner Georgeina Whelan said winds forecast for Tuesday were favourable but the fire remained unpredictable.
The agency said spot fires were likely to travel ahead of the fire driven by winds in the afternoon.
"We will experience moderate winds about 24km/h, however we will have gusts up to 40km/h, the peak period being between 10am and 2pm today," Ms Whelan said.
The fire danger is expected to reach severe on Tuesday.
Ms Whelan said several options had been developed to address the fire, taking into account the spotting, terrain, fuel load and unpredictable nature of fire activity seen during the bushfire season.
"We need the community to remain alert not alarmed," Ms Whelan said.
Ms Whelan urged people to monitor updates on the ESA website and social media channels and through local media.
"It is important that you don't rely on just one source of information," she said.
ESA held a community meeting in Tharwa on Tuesday morning. Another meeting will be held at the community centre at Uriarra at 6pm.
Residents near Tharwa have been urged to activate their bushfire survival plan. Those living in Banks, Calwell and Gordon have been advised to monitor the situation on the firefront.
The fire continues to burn in a south-east direction towards Boboyan Road.
People near Apollo Road and Top Naas Road are also affected by the blaze.
Bobyan Road is closed from the Namadgi Visitors Centre and south from Shannon Flat. Access to the areas is restricted to residents only.
No properties are currently under threat.
On Tuesday there were 15 fire crews on the ground including personnel from ACT Rural Fire Service, ACT Fire and Rescue and ACT Parks and Conservation. The Australian Defence Force is assisting.
Emergency text messages have been sent to 15,000 mobile phones in the area, alerting nearby residents to fire conditions.
ADF and State Emergency Services personnel started doorknocking on Monday and residents who have been advised of the emerging situation will have their properties tagged for recognition.
Ms Whelan said personnel had spoken to about 33 residents, landholders and their families.
The ESA advised residents in Tharwa and the remote area of Orroral Valley should:
- Activate your Bushfire Survival Plan if you have one
- If you do not have a Bushfire Survival Plan identify where you will go if you need to leave
- Go to esa.act.gov.au for regular bushfire updates
- Listen to your local radio station
- Bring your pets inside, close windows and doors to minimise smoke exposure
- Locate important documents, emergency kit, medication, animals, and family members
- Inform your family, friends, and neighbours of your plans and see if they need help preparing
- Moving your car outside if you have an electric garage door
- Arrange alternative transport in case of evacuation if you do not have access to a car
- Taking any additional action to protect your livestock and property.
A total fire ban has been declared for the ACT until midnight on Friday.
The territory is set to experience extreme heatwave conditions on Thursday and Friday with the temperature forecast to reach into the 40s.
Forecaster at the Bureau of Meteorology Abrar Shabren said winds would be milder in the morning on Tuesday before increasing later in the day.
"In the mid to later part of the day, we should see winds coming from the north-west around the 25 to 30km/h mark," Mr Shabren said.
"Around ranges in the ACT and the Brindabellas we should see higher wind speeds also coming from the west and as we go into the night they should start to ease off."
Mr Shabren said the fire danger would increase in Canberra later in the week as temperatures increase.
"The winds coming in from the north and north-west will bring hot and dry conditions and there's the possibility of elevated fire danger," he said.
"We'll see hot conditions and overnight minimum temperatures also being quite high."
The Mount Stromlo Observatory is closed on Tuesday, including to cyclists, due to the fire danger.