The incident occurred late Thursday near Buxton, around 100 km southwest of Sydney, when the firefighters' truck overturned after crashing into a tree, Efe news quoted the New South Wales (NSW) State Rural Fire Service as saying.
Firefighters were battling the fire at Green Wattle Creek, which on Thursday destroyed homes and posed a grave threat to the surroundings of the country's largest city.
These two casualties have brought the total death toll from fires in NSW up to eight since July.
Prime Minister Scott Morrison on Friday expressed his condolences for the deaths of firefighters and said their sacrifice to save lives and property would be "forever remembered."
"I express my sincere condolences and sympathies to the families of the firefighters who have so tragically been killed overnight. They were bravely defending their communities with an unmatched spirit and a dedication that will forever set them apart amongst our most courageous Austral," Morrison said in a statement.
The accident occurred shortly after NSW authorities declared a state of emergency due to a heat wave that on Wednesday caused the average temperature across Australia to reach 41.9 degrees Celsius, the second new record this week.
On Friday, the mercury was expected to hover around 40 degrees in most parts of the country, however, the authorities expect the brunt of the heatwave to be felt on Saturday, with the maximum temperature expected to touch 47 degrees in NSW.
"These fires and heat conditions are horrendous, and there are still difficult days ahead," said Morrison, who has been subject to much criticism for going on vacation to Hawaii amid the bushfire crisis in the country. He has also been lambasted for not dealing with the effects of the pollution caused by the smoke, as well as his pro-coal energy policy and lack of a climate plan.
"I deeply regret any offence caused to any of the many Austral affected by the terrible bushfires by my taking leave with family at this time."
( With inputs from IANS )