The Orroral Valley bushfire in the Namadgi National Park has burned almost one-fifth of the ACT but has so far been kept away from Canberra suburbs.

Key points: The Orroral Valley fire is downgraded to "watch and act" after earlier burning at an emergency level

The Orroral Valley fire is downgraded to "watch and act" after earlier burning at an emergency level Across the border in NSW, the Clear Range fire is threatening property in the towns of Michelago, Colinton and Bredbo

Across the border in NSW, the Clear Range fire is threatening property in the towns of Michelago, Colinton and Bredbo Authorities urge people in Tharwa, Banks, Gordon and Conder to leave if they feel unsafe, and ask all Canberrans to use less electricity

The out-of-control fire, which a military helicopter accidentally ignited this week, was downgraded to watch and act on Saturday evening after burning at emergency level earlier in the afternoon.

Emergency services warned people near Boboyan Road, Naas Road, Top Naas Road and Apollo Road to remain vigilant overnight, as conditions could change.

The fire is not currently posing a threat to the southern suburbs of the ACT, but authorities have urged people in the township of Tharwa and the southernmost suburbs of Banks, Gordon and Conder to monitor conditions.

The Monaro Highway connecting Canberra and Cooma is now closed. ( ABC News: Andrew Kennedy )

Meanwhile, New South Wales firefighters are continuing to battle the fast-moving, emergency-level Clear Range fire south of the border, which flared up when embers from the ACT blaze spread.

The Clear Range fire is threatening properties in Michelago, Colinton and Bredbo and the Rural Fire Services confirmed some properties had been lost in the Bumbalong area.

It is unknown how many properties have been destroyed or whether they were homes.

Residents in Michelago, Colinton and Bredbo have been told it is too late to leave and to seek shelter.

People in nearby Tinderry, Anembo, Jerangle and Chakola should be aware of embers being blown ahead of the main fire front.

For most of Saturday, the blaze also closed the Monaro Highway — the main connection between Canberra and rural communities to the south.

It has since reopened, but is under contraflow and could be closed again at short notice.

Sixteen aircraft are attacking both fires, along with ground crews from NSW, Queensland and Tasmania.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 1 minute 16 seconds 1 m 16 s Town of Bredbo under threat from bushfire

Earlier this week ACT Chief Minister Andrew Barr said the fires posed the greatest risk to Canberra since the deadly 2003 fire storm and that Saturday was going to be the "worst day".

"We acknowledge this is going to be a stressful day for residents, particularly in southern Tuggeranong," Mr Barr said on Saturday morning.

But Mr Barr also repeated earlier warnings to stay away from Namadgi, which has attracted "disaster tourists" throughout the week.

"I can't stress this enough: you are not needed, you are getting in the way, stay out of the area," Mr Barr said.

"It is incredibly disappointing that a number of people had to be told to leave the area last night by ACT police."

Embers may strike suburbs

Fire-spread predictions suggested in a worst-case scenario the blaze could grow up to five times in size on Saturday, sweeping through the ACT village of Tharwa and raining embers on Canberra's southernmost suburbs.

Instead, the fire continued its unpredictable behaviour, travelling in a south easterly direction and threatening towns across the border in NSW.

Firefighters in the mountain village of Bredbo, NSW, prepare for the approaching blaze. ( ABC News: Andrew Kennedy )

ACT ESA Commissioner Georgeina Whelan said, while the bushfire posed no immediate threat to Canberra suburbs, residents in Tharwa, Conder, Banks and Gordon could "leave the area if you feel unsafe".

An evacuation centre has been opened at nearby Erindale College.

The ACT Government said it had taken every step it could to avoid a repeat of the bushfires that devastated the city 17 years ago.

Mr Barr declared a state of emergency on Friday, giving the Government powers to direct residents and their livestock, seize control of property and access information.

Military personnel and ESA staff also doorknocked residents in the areas at risk, extra crews have flown in from interstate, and firefighters even managed to do some backburning this week.

Residents in rural areas and some suburbs have been asked to activate their bushfire plans. ( ABC News: Andrew Kennedy )

Horror of 2003 fires in residents' minds

When fires flared in the Namadgi National Park 17 years ago, few expected it to be as destructive as it was.

The firestorm took hold within 24 hours, and containing it became impossible.

It destroyed about 500 homes across Canberra's south-western suburbs and in rural communities. Four people died.

The 2003 firestorm swept into suburban Canberra, destroying about 500 properties. ( Getty Images: Daniel Berehulak )

This time, residents have been on alert for weeks, preparing their homes for what they fear will be a repeat of the 2003 event.

Mr Barr was keenly aware of this fear when he declared a state of emergency.

"I understand the anxiety that this announcement will cause, especially for those who lived through the 2003 bushfires," he said.

As in 2003, the surrounding land is extremely dry from years of drought, and the weather is forecast to be hot and windy.

Some Canberrans said they were exhausted not only from the weeks of preparation but also from the burden of those 17-year-old memories.

"It's just nerve-racking, just the waiting to see if it will happen or it won't happen," one Banks resident said.

Many have their cars ready and bags packed to evacuate if necessary.

Kim Moeller's home in Rosedale on the NSW South Coast was destroyed by bushfires earlier this summer. ( Supplied )

In the rural communities to Canberra's south, many people have left already, though some have chosen to stay and defend their properties.

Among them is Kim Moeller, a resident of Little Burra, who has already lost one home this season at Rosedale on the NSW South Coast.

"My plan is to stay and fight the fires. As long as it's not catastrophic, we think we're well prepared to be able to take on any fires," he said.

"I'm quite keen to defend and save this home."