At 11.50pm, a lightning strike on a tree during a fierce thunderstorm which swept across the Ellerslie Range east of Tarcutta on December 27, 2019, is suspected to have triggered the giant Dunns Road bushfire, which burnt almost 334,000 hectares during the Black Summer of 2019-20.

The fire destroyed 186 homes and 27 business premises across southern NSW, thousands of livestock and caused an estimated $56 million in damage. The fire also destroyed many of the historic huts in the Kosciuszko National Park.

A 47-year-old Goulburn man, David Harrison, died while helping to protect a friend's property near Batlow.

A public hearing into the 2019-2020 Black Summer bushfires commenced with an opening address at the Coroners Court of NSW, Lidcombe on August 25.

Public hearings have been scheduled to take place at various regional locations.

In September, the inquiry will travel to Cooma and Queanbeyan and in 2022 it will travel to other parts of regional NSW including Taree in March.

The inquiry is aimed at investigating over 40 blazes which burned through six per cent of the state, took 26 lives and destroyed nearly 2,500 homes.

Mid North Coast communities were among those who still bear the scars of one of the worst bushfire seasons in decades that claimed two local lives.

Giving evidence before State Coroner Teresa O'Sullivan at the NSW Bushfires Coronial hearing on Monday (September 20), NSW police detective Sergeant Sean Clarke told how he and RFS investigator John Baker had used supplied GPS coordinates of several lightning strikes to track the fire's source to a single tree in the forest.

The burnt tree was found in what was described as rugged and hazardous terrain. During two excursions on foot into the burnt-out area they systematically examined the area of interest for "macro and micro indicators" until they found a tree bearing distinctive scars.

Parallel scars on the tree and extruded sap indicated the tree had been hit by lightning.

"When a tree gets struck by lightning, generally they do one of two things: they explode or the heat internally fries the contents of the tree and superheat its interior," Sgt Clarke said.

"It's possible that one of the limbs [of the tree] had fallen off and triggered a fire."

The investigators found no evidence of human activity in the area, such as power lines, which may have been an alternative trigger factor.

The trigger for the Dunns Road has remarkable parallels to the 2003 firestorm which swept through Canberra's western edge in 2003.

In that event, a dry thunderstorm rolled in from the west toward the ACT on January 8 and with it, numerous lightning strikes. After that cell swept through, local farmer Wayne West, whose property Lazy Acres adjoins the Goodradigbee River, observed smoke coming from the area of McIntyre's Hut, in the Brindabella Ranges, and went to investigate the next day on his trail bike.

He found a tree smouldering but had no equipment on hand to extinguish it.

He told the resulting Coronial hearing that he had made dozens of calls to the NSW Rural Fire Service headquarters in Queanbeyan to get fire crews out to extinguish the fire but for three days, it burned unchecked.

On January 18, fanned by hot, dry winds, the firefront broke containment lines, joined with the Bendora fire and raced into Canberra, destroying hundreds of homes.

Like Canberra's 2003 firestorm, the Dunns Road bushfire of 2019 exhibited enormous speed as ambient temperatures rose and north-westerly winds increased.

The hearing was told that by December 28, the fire had fanned out in several directions.

The first day it took hold, it had travelled 19 kilometres. By the second day, it had spread 80 kilometres. In the meantime, a second dry thunderstorm had also swept through, creating hundreds of fresh ignition points.

In his evidence, NSW police fire investigator Detective Senior Constable Peter Alexander described how "there was no way they [the RFS] could prepare for 60 kilometres of fire travel in one day [December 30]".

By January 4, the Dunns Road fire had begun to merge with the smaller East Ournie Creek fire, to the south-west near the village of Tooma, to create what was later described as a megafire.

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