Joeleigh Esterhuizen, 8, of Macgregor  cools off in the family pool.

Joeleigh Esterhuizen, 8, of Macgregor cools off in the family pool. Photo: Melissa Adams

Canberra has sweated through another scorching day, while firefighters have battled a suspicious fire at Molonglo and several grass fires to the west of Canberra.

Canberra and the ACT was braced for another sweltering summer's day with the mercury forecast to hit 40 degrees, and at 2.40pm the temperature peaked at 40.1 degrees.

Earlier in the week, the temperature soared to 40.2 degrees on Wednesday, following a 37.3 degree day on Tuesday.

Cooling off in the Murrumbidgee River. From Royalla (from left) Phoebe Thompson 11, Sarah Thompson 17, Hannah Ferguson 17 and Bree Sturdess 17 and Sam Quirke age 17 of Calwell, on January 31. Click for more photos

Canberrans cool off in the summer heat

Cooling off in the Murrumbidgee River. From Royalla (from left) Phoebe Thompson 11, Sarah Thompson 17, Hannah Ferguson 17 and Bree Sturdess 17 and Sam Quirke age 17 of Calwell, on January 31. Photo: Katherine Griffiths

The overnight lows brought some relief, dropping to 15.3 degrees at 6am on Thursday.

Melbourne and Adelaide are also baking this week, with tops of 44 and 46 degrees forecast respectively for Thursday as the heatwave settles in over the south-eastern states. By 1pm, both had surpassed the 40-degree mark.

The forecast for the coming days

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Canberrans are in for another two days of temperatures in the high 30s before some cooler relief on Sunday.

Friday and Saturday both have forecast maximums of 39 degrees, with some showers developing on Saturday afternoon and evening.

There is also the possibility of showers on Sunday, when the mercury is expected to hit 30 degrees.

Monday will be cooler again, with a top of 25 degrees.

Fire bans in place

High temperatures and light winds prompted the authorities to declare a total fire ban for the ACT for Thursday, which has now been extended to 11.59pm Friday.

As part of Thursday's fire ban, Stromlo Forest Park was closed from 12.30pm.

The ESA warned that if a fire starts in these conditions, it may be uncontrollable and move quickly.

For more details on nature reserves and road closures as a result of the fire ban, visit the TAMS website.

Spin doctors converge

An army of government communications staff have been deployed to the ACT government’s Public Information Coordination Centre as Canberra continues to swelter and the territory faces a heightened fire risk.

Communications staff from all government directorates are working in the centre at Emergency Services Agency headquarters to ensure that if fires break out the public will be kept informed via the news media and social media platforms, such as Facebook and Twitter.

Fires sparked across the territory

Fire crews are on high alert as the territory and surrounding regions brace in severe fire conditions.

On Thursday afternoon Fire fighters have brought a blaze near the Kings Highway on the border between the ACT and NSW under control. 

A second fire also burnt nearby, on Powell Drive in Carwoola. It was reported at 2.40pm and two fire crews quickly brought it under control.

Meantime, fire crews were called to reports of fire at Bungendore and Pialligo on Thursday morning, but both were quickly ruled false alarms.

A homeless man is also facing questioning over two fires in Canberra, after he was found near the scene of a grass fire on Thursday morning with severe burns.

He has been airlifted to a Sydney hospital, with police keen to question him over his alleged involvement in the blazes.

Two fires were extinguished by firefighters on Wednesday afternoon.

The first blaze, about 500 metres south of the National Zoo and Aquarium was reported about midday.

At 2.30pm, another fire was reported near Geijera Place in Kingston about 2.30pm.

The cause of both fires on Wednesday was not known.

Suburbs set to swelter

Seven ACT suburbs will have power outages on Thursday as ActewAGL conducts scheduled maintenance.

The ACT Opposition Leader Jeremy Hanson has called on ActewAGL to "practise some commonsense" given the heatwave warning issued by ACT chief health officer Paul Kelly on Wednesday.

But Acting Chief Minister Andre Barr has defended the outages, telling The Canberra Times they were necessary and that residents had been notified "well in advance".

Have you been impacted by the power outages? Let us know: online@canberratimes.com.au.

Electricity, water usage soars

As the mercury climbs, Canberrans are using more electricity and water.

Electricity usage has been increasing, rising from 535MW at 6pm on Tuesday to 575MW at 4pm on Wednesday.

It is still a way off last summer's peak usage of 700MW on January 18, when it was 42 degrees.

A warning for parents and pet owners

The NRMA has issued a statement on Thursday, warning parents of the dangers of leaving children in cars.

With temperatures set to soar across the ACT and NSW on Thursday and Friday, the NRMA has warned that on a 44 degree day, it could reach 75 degrees inside a car.

Parents are also reminded that leaving an unattended child in a locked car is illegal, with fines of up to $22,000 under the Children and Young Persons Act 1988.

Pets and animals cool off

It's not just us humans seeking cool relief in the heat - zookeepers at the National Zoo and Aquarium have been busy finding ways to keep their furry friends happy.

Photographer Katherine Griffiths headed out to the zoo on Wednesday and got some amazing photos of the animals being given ice blocks containing their favourites treats.

It was as much about hydrating the animals as it was about entertainment for visitors and zoo staff.

Cheetahs, meerkats, giraffes and even koalas got in on the action - check out all the photos here.

And authorities have warned pet owners to ensure they've got access to shade and water throughout the hot conditions.