The 19-month-old son of a firefighter killed while battling Australia's bushfires received a posthumous medal to honour his father's bravery on Thursday.

Powerful images from the funeral of Geoffrey Keaton -- one of two firefighters killed while fighting bushfires on December 19 -- were posted by New South Wales Fire Service.

Harvey, Keaton's young son, was dressed in a firefighter outfit with a pacifier in his mouth as New South Wales (NSW) Rural Fire Service Commissioner Shane Fitzsimmons pinned the medal to his chest.

His 32-year-old father had been awarded the posthumous Commendation for Bravery and Service after he and his colleague Andrew O'Dwyer died last month.

They were killed by a falling tree that hit their vehicle, causing it to overturn.

"Today the NSW RFS family farewelled one of their own, with the funeral of Geoffrey Keaton held in western Sydney earlier today," a NSW Rural Fire Service Facebook post read.

Photos posted on the fire service's Facebook page show hundreds attending the funeral, many donning yellow RFS uniforms and a guard of honor forming as Keaton's hearse arrived.

Another poignant photo shows a mug placed on his coffin, with the words: "Daddy I love you to the moon and back!," inscribed on it.

Many people commented on the posts, paying tribute to Keaton's "heroic efforts."

Parts of Australia have been devastated by bushfires for months, with the states of New South Wales and Victoria being hit particularly hard.

At least 17 people have died across the country so far and it is feared that the fires are not about to stop anytime soon.

On Thursday, NSW declared a state of emergency for the third time in as many months as emergency crews battle deadly blazes and prepare for a dangerous weekend ahead.

Australian Prime Minister Scott Morrison and his wife, Jenny attended Keaton's service.

He tweeted: "This morning Jenny will join me as we remember and give thanks for the life and service of Geoff Keaton at his memorial with his partner Jess, his son Harvey and all his family and friends, especially those from the Horsley Park RFS Brigade."

Morrison has come under pressure for his handling of the bushfires -- and the climate crisis more generally.

Morrison faced tough questions on Thursday from those living in the middle of the bushfire danger zone.

One woman said she would only shake his hand in order to get more money for the Rural Fire Service while another group yelled out "you're an idiot" and "piss off" as he walked away from them while on a stop in the town of Cobargo.

Morrison said his government aimed to "meet and beat our emissions reduction targets" -- but added that it would stick to "sensible" policies that "don't move toward either extreme."

The NSW Rural Fire service has set up dedicated bank accounts to collect donations for the families of volunteer firefighters who have been killed while on duty this fire season.