Fire crews are working to contain an out-of-control bushfire burning in the Namadgi National Park, ahead of a challenging week of conditions for firefighters.
The Orroral Valley fire is now five kilometres from Tharwa and eight kilometres from Banks in the southern part of Tuggeranong. The blaze has burnt 10,492 hectares as of 1.30pm on Wednesday and continues to grow in size.
It was downgraded overnight from a watch and act level to advice on Thursday about 1.30pm.
The fire is burning in a north-east and easterly direction towards Mount Tennent, Tharwa, Boboyan Road and Top Naas Road. There has also been an increase in fire activity to the western side of the firefront.
Fire authorities say there is limited activity to the eastern side of the fire but the fire remains active to the north of the fireground.
ACT Chief Minister Andrew Barr told the media on Wednesday afternoon the fire would not be able to be extinguished for some time.
"This is a challenging day and we have challenging days ahead," Mr Barr said.
Spotting from the fire was seen on Tuesday night on Mount Tennent and there were reports of spotting on the outskirts of the town of Tharwa.
Residents in Tharwa, Boboyan Road, Apollo Road and Top Naas Road have been urged to remain vigilant. Those living in Banks, Gordon, Conder, Calwell and Theodore should continue to monitor conditions.
No properties are immediately under threat on Wednesday morning.
The community needs to be comfortable with being uncomfortable and the fire will take some time to be extinguished.ESA commissioner Georgeina Whelan
The ACT's specialist intelligence gather helicopter will be conducting aerial surveillance throughout the day.
Firefighters are patrolling the fireground and preparing for property protection.
ACT Emergency Services Agency commissioner Georgeina Whelan said conditions had been more moderate overnight, allowing crews to set up containment lines.
"We've just had additional activity to the west of the fire and that's concerning for us and that's getting the fire into the national park and moving it in a westerly direction, based on current winds," Ms Whelan told ABC radio on Wednesday morning.
"It gives us an opportunity to work on containment today.
"The fire continues to grow, and what we want to do is to take advantage of the conditions and work on containment and access lines around fire trails and fighting the fire on the ground of our choosing and allows us to stop the flow of it into suburban areas."
Prime Minister Scott Morrison said the fire was "a reminder again that we're a long way from the end of this bushfire season".
"I extend all my sincere sympathies to those particularly around the capital today on what has been a difficult night," he said.
People in Tharwa were told to evacuate on Tuesday evening at the height of fire activity, and on Wednesday authorities told them "If you do not need to be in this area, it is still best for your safety to not enter or return."
About 15 people spent the night at an evacuation centre at Erindale College, while a number of Tharwa residents chose to stay to defend their properties.
Evacuees have been told they can return home on Wednesday, but fire authorities have warned an evacuation order may be issued again later in the day on Wednesday.
Large amounts of smoke can be seen around Tharwa.
ACT SES members, ACT Fire and Rescue units, ACT police and Australian Defence Force personnel are out doorknocking on Wednesday in southern parts of Tuggeranong, including in Banks, Gordon and Conder.
The fire was likely started by the landing light of an MRH-90 Taipan helicopter, whose crew was working in the national park to clear landing zones for other aircraft.
The incident is under investigation.
The Department of Defence said the helicopter became alight within 12 seconds of the incident starting.
There were 12 people onboard the helcio
The agency's commissioner would not comment further on the incident but said it was an unfortunate event.
Ms Whelan said Wednesday would be a crucial day to work to contain the fire with serve heatwave conditions forecast for later this week.
The Bureau of Meteorology has forecast for temperatures to reach 39 on Thursday before getting to a high of 42 on Friday and Saturday with no chance of rain. The conditions will be further exacerbated by low humidity.
The ESA has said a total fire ban will be in place for some time.
"Wednesday is a day where we can be a bit constructive with the fire and the conditions, but we're not going to put the fire out any time soon," Ms Whelan said.
"The community needs to be comfortable with being uncomfortable and the fire will take some time to be extinguished.
"Wednesday will be about putting containment lines in and putting access routes in so when the fire comes out of the high country, we can attack it in a safe manner."
Large air tankers will be working throughout the day, dropping water and fire retardant onto many areas of the fire that remain inaccessible.
Ms Whelan said while conditions are more moderate on Wednesday, the blaze could still jump back to an emergency level during the day.
"I never say never to that possibility. What we're asking the community to do is to stay alert and these conditions are unpredictable and we're monitoring them closely."
Several roads in the area remain closed, including the Tharwa Drive roundabout at Knoke Avenue, Angle Crossing at the Monaro Highway, Boboyan Road from the Namadgi Visitors Centre and Tidbinbilla Road from Point Hut Road.
Ms Whelan has urged residents travelling south to see the fire and take photos of it to avoid the area.
"It gets to a point where it puts lives at danger and limits the response of emergency services and police," Ms Whelan said.
"If you don't need to be in the area where there's fire danger, don't be there, stay home and stay safe."