A young man killed in a garbage truck tragedy in Western Sydney has been remembered as a big-hearted person who had donated bone marrow to his brother before his death. 

Nathan Hearne, 21, was hit by the truck outside a restaurant on Luxford Rd in Mount Druitt about 2.20am on Thursday.

WATCH THE VIDEO ABOVE: Man dies after garbage truck accident in Mount Druitt

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Paramedics desperately tried to save him, but he died at the scene.

Hearne’s devastated mother Leanne Whelan told 7NEWS.com.au that he once donated bone marrow to help his sick brother.

“He had the biggest heart,” Whelan said.

“He donated bone marrow for his brother last year.”

Hearne once donated bone marrow to help his sick brother. Credit: Facebook

The extraordinary act came as Hearne’s two brothers battled Familial Hemophagocytic Lymphohistiocytosis type 5 (FHL-5), an extremely rare inherited immune disorder.

A GoFundMe set up to support the family said brothers Stevie and Colton are the only siblings formally diagnosed with the condition in Australia.

Stevie underwent a bone marrow transplant at The Children’s Hospital at Westmead last year, while Colton is currently in hospital recovering from the same procedure.

Amid the family’s latest heartbreak, Whelan remembered Hearne as a “joker” who loved his girlfriend, Amy.

Those who knew the 21-year-old painted a picture of a kind and caring man who was always deeply loved. 

Hearne’s mother said he had “the biggest heart”. Credit: Facebook

Family friend Jessica Carter described Hearne as a “vibrant, outgoing, cheerful spirit who made everyone who met him remember him”.

“He was always ready to lend a helping hand and a great mate to those who knew him,” she said.

“You will be deeply missed Nathan by ALL that met you and the MANY MANY people who loved you.”

Another friend said she had been “rocked” by his sudden death.

“He was a beautiful soul, a gentleman, and a good mate, he will be greatly missed,” the friend said. 

Questions over hours before death

A critical incident investigation has now been launched into the circumstances surrounding Hearne’s death after police revealed he had interacted with officers in the hours beforehand.

Police said Hearne attended the rear of Mount Druitt Police Station twice during the evening and interacted with officers.

A critical incident investigation is underway. Credit: 7NEWS

Whelan has since raised concerns about those interactions.

The 31-year-old garbage truck driver was uninjured and was taken to hospital for mandatory testing.

A critical incident investigation team from Riverstone Police Area Command will investigate the circumstances surrounding the incident.

The investigation will also be independently reviewed by the NSW Police Professional Standards Command and overseen by the Law Enforcement Conduct Commission.