ACT Emergency Services Minister Mick Gentleman said Canberrans would need to be prepared should a decision be made to elevate a state of alert to a state of emergency.

The ACT has been in a state of alert for most of January.

"We've been timely with the announcements about the various states over the last couple of weeks," Mr Gentleman said.

"It may well be that because of the conditions over the next few days we may need to go to a state of emergency."

A declaration of a state of emergency occurs if the Chief Minister is satisfied that an emergency has happened, is happening, or is likely to happen.

It allows a nominated emergency controller powers to manage the region in the area of emergency.

This includes control over the movement of people, taking possession of any premises, animal, substance or thing in or near the emergency area, and directing people to provide information or produce documents or anything else reasonably needed.

The fire in the Namadgi National Park continues to burn out of control and has burnt more than 15,000 hectares.

As of 2.30pm on Thursday, the main fires are 3.3 kilometres away from the town of Tharwa with spot fires 2.1 kilometres away.

ACT Emergency Services Agency Commissioner Georgeina Whelan said the fire was nine kilometres away from the southern suburbs of Tuggeranong such as Banks.

It's predicted the fire could cross the border into NSW on the eastern side of the firefront.

The fire has crossed Rendezvous Creek to the south of the blaze.

It's estimated 50 firefighters are tackling the blaze, assisted by 14 vehicles and eight aircraft.

"We could see a significant spread of the fire in the south-east into NSW over the next 48 to 72 hours," Ms Whelan said on Thursday afternoon.

"We continue to monitor spotting to the north-east.

"The fire is spreading slowly at the moment, but consistently in all directions."

The Orroral Valley bushfire may encroach further towards Tharwa and southern Canberra suburbs in the next 24 hours, as firefighters warn of "unprecedented" conditions.

Authorities say the fire is moving in a south-easterly direction towards Tharwa and also in a westerly direction further into the Namadgi National Park.

Fire authorities say while there is limited fire activity on the northern and eastern fronts of the fire, there has been an increase to the west of the blaze.

Temperatures were set to reach 37 degrees on Thursday before rising to 41 on Friday and 42 on Saturday.

Wind gusts of up to 50km/h are expected on Saturday and this is expected to exacerbate conditions on the fireground.

Backburning was carried out on Wednesday evening during a lull in conditions to help strengthen containment lines ahead of the deteriorating weather this weekend.

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Overnight, four NSW firefighters were taken to hospital after a tree fell on a fire tanker about 10.30pm.

Three firefighters suffered non-life threatening injuries and the fourth was uninjured. All four were taken to Canberra Hospital, where they are in a stable condition.

Three of the four crew members were from the Jerrabomberra Creek RFS brigade.

NSW Rural Fire Service spokeswoman Angela Burford said multiple NSW crews were assisting ACT colleagues in fighting the bushfires.

Efforts would be stepped up in coming days as conditions were set to deteriorate.

Waterbombing efforts have been carried out to protect valuable assets in the Namadgi National Park, including the Orroral Homestead and communication lines.

Community meetings will be held at Uriarra Village at 6pm on Thursday and in Tharwa at 10am on Friday.