The fire tower had been evacuated earlier in the week and since then the mountain had been a brooding menace of smoke, with thicker plumes where the undergrowth was cooking and waiting for its next trigger.

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Chatting around their fire truck on the Apollo Road, 15km south of Tharwa, and watching the mountain, it was one of the Queenslanders who first noticed the subtle change in direction and tempo of the wind.

Right on cue, a clot of ash fell from the sky.

"Hmm," he said. "This could get interesting."

And sure enough, 30 minutes later, it did.

Fanned by a strengthening north-west wind, one of the foothills of Mt Tennent erupted about 2.30pm, the smoke plumes thickening, blackening and spreading within a matter of minutes.

To these Queensland Fire Service strike teams, 74 members in total with 13 trucks and two command vehicles, it's their turn to return a favour or two.

In the volunteer rural firefighting world, the generous sharing of resources in times of need across jurisdictions took on a whole new relevance on Thursday when the procession of four-wheel drive fire trucks painted in unfamiliar bright yellow rolled into Canberra's most exposed southern suburb with all lights flashing.

The Queenslanders arrived in Tharwa after significant firefighting across numerous NSW South Coast fire fronts, from Nowra to Ulladulla, in recent weeks.

The crews will work deep into the night in the foothills, return to Canberra each night to bunk down, then tag-team with replacement QFS members.

Their fire trucks are sourced from all over south-east Queensland, with various brigades each surrendering a vehicle to support the NSW and ACT causes.

Two of the trucks and teams have gone down to Bega, while the rest are being assigned to property protection duties south of Tharwa as Saturday's severe fire weather looms.

"We'll be relying a lot on the locals here for advice on the conditions and the landscape," strike team leader Rob Sargent said.

"But that's always the way when you're working someone else's patch.

"We're pleased to help out. We had RFS guys from down here come up to help us out when we were stretched in manpower by some big fires at places like Warwick and Binna Burra back in September last year.

"So for us, this is returning the favour."

For one of the team members, Tony Shaw from the sleepy Queensland hamlet of Narangba, north of Brisbane, it's his first time back since helping to fight the 2003 Canberra bushfires.

"These weather conditions do feel a little similar," Mr Shaw said.

"But like everyone here, we're hoping it never gets that bad."

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