One-year-old Charlotte wore her dad's large white helmet on her small head during the volunteer firefighter's funeral where she and other mourners were told Andrew O'Dwyer died a hero.

Mr O'Dwyer, 36, was killed in mid-December when his NSW Rural Fire Service fire truck rolled while battling the large Green Wattle Creek blaze southwest of Sydney.

RFS commissioner Shane Fitzsimmons choked up as he spoke directly to young Charlotte on Tuesday at Our Lady of Victories church in Horsley Park.

"You need to know that your dad was a selfless man, he was a special man, and he only left us because he was a hero," Mr Fitzsimmons told the congregation.

The toddler – who was wearing a white dress with silver sandals and had her hair in pigtails – at one stage touched her father's casket before wandering up to the pulpit.

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Inset: Andrew's cherished daughter Charlotte at her father's casket. Photo: ABC

Volunteer Geoffrey Keaton, 32, who was killed in the same crash, was remembered at a separate service last week.

Hundreds of family, friends and RFS members filled the Horsley Park church on Tuesday not far from where Mr O'Dwyer's brigade is based in Sydney's west.

Prime Minister Scott Morrison, NSW Premier Gladys Berejiklian, state Emergency Services Minister David Elliott and NSW Police Commissioner Mick Fuller were among the mourners.

RFS volunteers and representatives from other emergency service agencies formed a guard of honour as Mr O'Dwyer's casket was carried into the church.

Some saluted. Others placed their hands on their heart.

Church bells tolled as Mr Fitzsimmons presented commendations for extraordinary service and bravery to Mr O'Dwyer's partner, Melissa, who also joined the local brigade in 2015.

"There are no words that can adequately describe our sorrow, our respect, our regard, for the loss of Andrew," the commissioner said.

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Inset: Mr O'Dwyer lost his life in December. Photo: RFS

The commissoner pinned Mr O'Dwyer's service medal on Charlotte's dress and then his white RFS helmet was placed on the toddler's head where it remained.

Errol O'Dwyer said farewelling his son was one of the hardest things he'd ever done. He described Andrew as a free spirit who lived in the moment.

His greatest achievement came "with the birth of his daughter Charlotte – the apple of her father's eye," Errol said.

"You will live in our hearts forever. Although my heart is broken you have made me very proud."

Horsley Park captain Darren Nation said Mr O'Dwyer's love for the fire brigade was "as thick as the blood that ran through his veins".

He loved his wife and his daughter and "everything that he did, he did for them," Mr Nation said.

"I am grateful that Andrew's memory will live on in his daughter".

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Inset: Prime Minister Scott Morrison hugs Horsley Park RFS captain Darren Nation at the funeral. Photo: ABC

Mrs O'Dwyer walked behind her husband's casket – draped in an RFS flag – as it was carried out of the church after the service.

As mourners converged to greet the family, Charlotte cried.

Mr Morrison, who attended with wife Jenny, gave a long hug to her mother.

Hundreds of family, friends and RFS members filled the church – still decorated for Christmas – as tributes flowed for the young father.

Prime Minister Scott Morrison, NSW Premier Gladys Berejiklian, state Emergency Services Minister David Elliott and federal Labor MP and local member Chris Bowen were among the mourners.

Volunteer Geoffrey Keaton, 32, was killed in the same crash and was remembered at a separate service last week.

RFS volunteers and representatives from other emergency service agencies formed a guard of honour as Mr O'Dwyer's casket was carried into the church, with some saluting and others placing their hand on their heart.

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Inset: RFS commissioner Shane Fitzsimmons with Andrew O'Dwyer's daughter Charlotte.

Church bells tolled as Mr Fitzsimmons presented a commendation for extraordinary service to Mr O'Dwyer's partner Melissa.

Mr O'Dwyer's father Errol said farewelling his son was the hardest thing he had ever done and described his son as a free spirit who lived in the moment.

His greatest achievement came "with the birth of his daughter Charlotte, the apple of her father's eye"," Errol said.

"Although my heart is broken, you have made me very proud," he said.

Members of the Maori community performed a haka outside the church following the service as a sign of respect, before Mr O'Dwyer's casket was driven away. It's understood his best friend is Maori.

Mr Morrison, who attended with wife Jenny, gave a long hug to Melissa.

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Inset: A haka is performed at Andrew's funeral. Photo: ABC

-AAP