A fire burning in Canberra's south-east is at advice level after earlier forcing the cancellation of most incoming and outgoing flights at the nearby airport.

Key points: The fire threatened properties Wednesday and flared up again Thursday afternoon

The fire threatened properties Wednesday and flared up again Thursday afternoon Just after 2:00pm the fire merged with a second fire in the same suburb

Just after 2:00pm the fire merged with a second fire in the same suburb The combined fire is called the Beard fire and is currently at advice level

The Beard fire, which first flared on Wednesday in Redwood Forest in Pialligo, jumped the Molonglo River on Thursday and came close to the suburbs of Beard, Harman and Oaks Estate.

It also merged with a second fire on Kallaroo Road, which began in the same suburb of Pialligo earlier in the day.

The combined fire reached 424 hectares in size and was at emergency alert level for much of the afternoon, but by 9:00pm was down to 379 hectares.

At about 4:50pm on Thursday, the ACT Emergency Services Agency (ESA) downgraded the fire to watch and act, before downgrading again to alert level at 8:45pm, confirming the fire was being controlled.

They also confirmed some businesses had been damaged by the fire, but no homes.

All flights in and out of Canberra Airport were cancelled due to a bushfire burning nearby. ( Supplied )

On a day when six emergency fires were at one point burning across New South Wales, temperatures soared and some properties were lost at the South Coast towns of Moruya and Bermagui.

And just after 2:00pm, the NSW Rural Fire Service confirmed three American firefighters had died after a Large Air Tanker crashed while fighting one blaze in the Snowy Monaro area.

Due to the Beard fire the Canberra Airport was closed to arrivals and departures for much of the day, but services resumed for some Qantas flights in the late afternoon.

In a tweet, the airport said it had not been evacuated, but advised people to contact their airline for updated information.

By early evening, the advice from the ESA to people in Pialligo and at Brindabella Business Park, near the Canberra Airport, was that they were safe where they were, and should monitor changing conditions.

A firefighter at the Beard blaze, near Oaks Estate. ( ABC News: Jordan Hayne )

Those who had left as a precaution were told it was safe to return to their homes.

People in Beard, Harman, Oaks Estate and Crestwood — who were earlier advised to seek shelter and told it was too late to leave — were told they should stay indoors due to hazardous smoke burning in the area.

But at 9:00pm, the ESA said atmospheric monitoring had been conducted and the air quality was safe.

The hazardous smoke was caused by the recycling centre on Underwood Street in Beard being impacted by the fire.

ESA website goes down in middle of emergency

Smoke covers the Canberra suburb of Beard, significantly reducing visibility. ( ABC News: Tom Lowrey )

The ESA said due to a system failure their website was not operational for three hours, at the beginning of which the fire was at an emergency level.

"The hosting capability for our website is down and that is affecting a number of websites across NSW," ESA Commissioner Georgeina Whelan said at the time.

"So we will be keeping you up to date via Facebook live and obviously through our partners at ABC."

A 737 water bomber from the Richmond RAAF base also assisted with firefighting efforts.

One firefighter suffered minor injuries while battling the blaze but was able to resume his role later this evening.

Oaks Estate Road remained closed between Pialligo Avenue and Railway Street, with all other road closures in place that afternoon lifted.

The fire could be seen burning close to Brindabella Business Park. ( Facebook: Stephanie Edwards )

There were two relief centres in place over the afternoon, one in the ACT and one in Queanbeyan.

In the ACT, the relief centre was at Dickson College for people from the fire affected-areas. It was accessible for people with disabilities and was also receiving domestic pets.

The second relief centre was at Queanbeyan Showground.

Juanita, Kyah and Braeden Wolf and dog Pepper evacuated their home due to the emergency fire at Beard south of Canberra Airport. ( ABC News: Elise Fantin )

Crestwood residents Juanita, Kyah and Braeden Wolf evacuated there on Thursday afternoon with their dog Pepper, saying they preferred to be "on the safe side".

"With the wind you never know what might happen," Jaunita said.

"I was working in Fyshwick so I was watching [the fire] grow, just watching the smoke get thicker and thicker."

The family said they would wait out the emergency at the showground, where they felt safe.

"Considering what has happened in other places … you never know what might happen," she said.

"So it is very scary."

The Kings Highway, which was also closed north of Batemans Bay due to the Clyde Mountain bushfire, later reopened.