Crews battled for hours against the blaze which extended across bush land from just east of the airport to the Oaks Estate.

At one stage, at least four helicopters were water-bombing intense outbursts of fire. Both the ACT and New South Wales Rural Fire Services were active.

Homes were evacuated and a pall of acrid smoke hung over a large section of the east of the city and Queanbeyan.

The fire was upgraded to "emergency" level at 5.20pm after it crossed the Molonglo River but was downgraded to advice shortly after 7pm.

ACT ESA incident controller Matthew Mavity credited "early detection and lots of units" for being able to contain the fire so rapidly.

An airport control tower spotted the fire shortly after it broke out and the airport's fire crew was dispatched immediately, he said.

The fire was fueled by dry African lovegrass and fanned by north-westerly winds.

Crews worked to build in-depth containment lines overnight and patrolled the perimeter, extinguishing hot spots.

Mr Mavity said 40 units were working on the fire - 25 units on the northern sector and 15 units on the east.

"I would never say the threat is over but we will continue to have crews working and patrolling overnight to strengthen containment lines and use specialist equipment to monitor the fire," he said.

While fire conditions are expected to be challenging on Friday, Mr Mavity said he had the resources to deal with the threat.

As of 8.30pm, it had burnt out nearly 150 hectares. No homes were damaged although it came within metres of the water treatment works substation.

Witness accounts show just how fast the fire was moving - and how quickly crews moved to combat it.

Firas Ajaj arrived at his warehouse at Beard at 4.30pm and saw the smoke. Fifteen minutes later, he saw flames, and was cut off from leaving.

"It spread fast," Mr Ajaj said. "There are some strong winds."

The fire and the intense effort to contain it underlined a message earlier in the day that Canberra should be braced for another "extreme weather event" as winds whip up across the territory today and tomorrow.

Chief Minister Andrew Barr said before the fire, "we are maintaining a state of high alert in the rural areas of the ACT".

The Emergency Services Agency said there was no formal state of alert for the suburbs.

But high winds were expected across the territory, with a danger of falling trees and branches. Residents were urged not to park cars under trees.

High winds would also heighten the fire danger. There was a total fire ban across the ACT on Thursday from midnight to midnight.

In the wake of yesterday's fire and those of the past months as well as hail and wind, Mr Barr described "a summer of unprecedented weather events". He thought there was more to come in "a long summer".

A close watch is being kept on fires close to the western ACT borders.