As predicted, Canberra Airport has surpassed the highest officially recorded December temperature in the ACT, amid a heatwave that continues to sweep the country.

Key points: Several December temperature records are forecast to be broken as the heatwave continues

Several December temperature records are forecast to be broken as the heatwave continues Canberra faces three successive days of record forecasts

Canberra faces three successive days of record forecasts A cold front will move into WA late today, bringing comparatively cooler temperatures

At 3:16pm, the Bureau of Meteorology (BOM) reported the mercury had reached 39.3C at Canberra Airport, breaking the 1994 December record of 39.2C.

The temperature is predicted to peak at 40C in the ACT, but today's new record may not last long; a top of 41C is forecast for Friday, and again on Saturday.

"We're looking at Friday and Saturday as being even hotter," Mr Bennett said.

"It may be a very short lived [record], and we could see it go on Friday and then we could see it go again on Saturday."

Earlier forecasts for Saturday put the station's hottest temperature ever, 42.2C, under threat of being overtaken, but the BOM later downgraded its prediction to 41C.

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Three states in Australia reached maximum temperatures of more than 47 degrees Celsius yesterday, amid a massive heatwave.

The highs — recorded by the BOM at Fitzroy Crossing in Western Australia, Wudinna in South Australia, and Birdsville in Queensland — came one day after what preliminary data suggested was the hottest day on record in Australia.

But Mr Bennett said today was predicted to bring record-breaking temperatures for many areas of the country.

"We feel that [on Thursday] we'll probably start to see more records being broken for December as that heat builds on into Victoria and NSW," he said.

The mass of hot air lingering over swathes of Australia meant the newly set record of hottest Australian day could be surpassed before the heatwave was through, Mr Bennett said.

"The extent of the heatwave is pretty remarkable so we couldn't rule it out," he said.

"It may be that the peak is today."

However cooler temperatures seeping into parts of the country today could bring the overall average temperature for the country down.

Phoebe and her grandmother found an oasis at Canberra's Dickson Pool on Wednesday. ( ABC News: Alexandra Alvaro )

"It may be that we start to see a decrease in the area [of heatwave conditions] as we move through Thursday," Mr Bennett said.

"Certainly there are some significantly cooler changes moving into parts of WA for example tomorrow."

That cold front is expected to reach South Australia late on Friday, but respite is not expected to reach the eastern states until late on Saturday.

Take care of all the members of your family

As in prior heatwaves, the advice from experts is to cancel any "outdoor exertion" once temperatures hit 38C, stay indoors, and stay hydrated.

The same advice can be applied to your pets.

"Treat them as you would yourself or your children," Geoffrey Rutledge from the ACT's Environment, Planning and Sustainable Development Directorate said.

"Make sure that you've got heaps of water for them, and give them a spray of water as well."

Erin Gillan has had to come up with innovative ways to keep her pets cool in summer. ( ABC News: Kate Midena )

Vet Nurse Erin Gillan owns a dog and two cats, and lives in a rental property with poor cooling.

"Heatstroke is a very real issue, a very real concern," she said.

"They've got no way of cooling down when there's nowhere cool in the house to get to to get away from the heat."

When the temperatures get high, Ms Gillan has a special jacket for her dog that can be wet with water to keep him cool.

"I actually once put a pool in the kitchen for him with towels, so he had water to get into," she said.

She has also taken several measures to keep the house cool when she is not at home.

"I've put a special removable film on the windows to try and reflect the sun, extra curtains, and I bought a portable reverse cycle air conditioner to put in the lounge which I can monitor remotely," she said.

For all the members of your family, there are several measures that can be taken to keep your house as cool as possible.

"The easiest thing is to close your house up during the day, close your curtains and shade your windows, and then open your house up at night and try and get some cool breeze in," Mr Rutledge said.

"A pedestal fan is also a very good and a very effective cooling agent."

Editor's note, 3 January 2020: This story was amended to clarify that temperatures given for Canberra refer to readings at the official BOM station at Canberra Airport. Higher temperatures from former stations that are no longer used by the BOM for official record keeping have been recorded in the past.