Dire Warning As ACT Faces Worst Fire Emergency Since 2003 Crisis

Residents in the nation's capital are bracing for dangerous fire conditions over the coming hours as an out-of-control fire threatens lives, with some communities told it's too late to leave.

The Orroral Valley Fire is continuing to burn at an emergency level in the ACT  with residents in the Tharwa Village, Boboyan Road, Appollo Road and Top Naas Road, told to seek shelter immediately.

ACT Chief Minister Andrew Barr said it was the worst situation the region has faced "since the 2003 bushfires."

"If you are not in the area, do not return," the ACT's Emergency Services Agency said on Tuesday afternoon.

"The fire may pose a threat to all lives directly in its path. People in these suburbs are in danger and need to seek immediate shelter as the fire approaches."

Residents in  Banks, Conder, Gordo, Smiths Road and the remote area of Orroral Valley have been told to activate their bushfire survival plans and stay alert as authorities begin door-knocking operations.

It comes as authorities said a defence helicopter's landing started the blaze south of Canberra, which has now doubled in size.

The defence chief of Operation Bushfire Relief Lieutenant General Greg Bilton said the fire started after a reconnaissance helicopter landed.

He said the heat of the landing light likely started a grass fire under the chopper, growing rapidly and damaging the helicopter before it took off.

The out-of-control fire, which is travelling in a northeast and easterly direction, has been burning at emergency level for a number of days and has grown to over 8,000 hectares.

"Under current conditions, a fire is difficult to control," the ESA said.

Warnings have also been issued for embers well ahead of the main fire front which are starting spot fires and bring further threats to properties.

"There has been significant activity in the fire ground as the cloud cover has lifted this afternoon," Commissioner Georgeina Whelan told reporters at a media conference on Tuesday afternoon.

"There is significant spotting ahead of the fire, in some cases up to 5km. We can expect this fire behaviour to continue until well into the evening."

Whelan said conditions are very dangerous but authorities have been preparing for these conditions "for several weeks."

"Firefighters may be unable to prevent a fire from reaching your property. You should not expect a firefighter on your door," Whelan said.

"On our worst fire day, I will not be able to put a fire truck on every corner. So now it's about working together to keep our community safe."

There is currently no threat to Canberra suburbs -- which have been heavily impacted by smoke from the fires -- but Canberrans are being warned to stay on alert.

Authorities are now also concerned about changing wind conditions with stronger gusts likely to make conditions even less favourable for firefighters, as gusts of up to 40 kilometres an hour increase fire activity on the ground.

"As a consequence, the smoke plumes that you are seeing have been increased because this fire is creating its own weather pattern," Whelan said.

"This is creating local fire winds and dangerous and erratic fire behaviour."

Smoke rising from the Namadgi National Park fire burning south of Canberra. Image: AAP.

"We, across the ACT, are now experiencing what our colleagues in Victoria and New South Wales have been experiencing for several weeks and that is, hot, dry weather, with enormous fuel-loading," Whelan said, adding that a total fire ban would remain in place," for the foreseeable future.

Emergency services have 27 vehicles, five helicopters, three small planes, two large air tankers and one very large air tanker fighting the fire.

Defence personnel have been deployed to help build containment lines and assist in operations.

An Evacuation Centre is now open at Erindale College for rural residents at 115 McBryde Cres, Wanniassa ACT.

With AAP.