The 59-year-old NSW National Parks firefighter was struck by a falling tree about 10.45pm on Sunday while patrolling a fireground and is believed to have suffered a cardiac arrest.
Colleagues performed CPR until paramedics arrived, but he died at the scene of the Bulahdelah bushfire on the NSW Mid North coast.
The man was a divisional commander in the National Parks and Wildlife Service who joined the organisation in 1996.
His death is the first time a National Parks firefighter has been killed on a fireground since 2011.
"This particular person has paid the ultimate sacrifice in trying to protect the community," NSW Emergency Services Minister Jihad Dib told reporters.
"The best thing that we can do to honour these memories ... is to make sure we take every action we can to prevent them being in this situation."
Prime Minister Anthony Albanese also offered his condolences to the firefighter's family and colleagues.
"This terrible news is a sombre reminder of the dangers that our emergency services personnel face to keep our homes and communities safe," he said in a statement.
The NSW Rural Fire Service confirmed 20 homes were destroyed between the Bulahdelah fire and another fire at Koolewong on the NSW Central Coast.
More than 50 fires were burning across NSW as of about midday on Monday, with nine uncontained.
There was s a real risk of bushfire complacency among the community after several seasons of reduced activity, the RFS commissioner said.
"We know that after a few years of elevated rain and wet conditions, people aren't thinking about bushfires sufficiently," Trent Curtin said.
"Embers can travel long distances - as we saw in Koolewong this week - where an ember moved a kilometre from one peninsula to another."
Federal and state disaster assistance funding has been activated across the Central Coast, Mid Coast, Upper Hunter, Muswellbrook, Warrumbungle and Dubbo.
More than 250 firefighters, 50 trucks and nine aircraft battled the Koolewong blaze at its peak where 16 homes were destroyed in an hour.
Meanwhile in Tasmania, authorities confirmed a 700-hectare blaze at Dolphin Sands, near Freycinet National Park on the state's east coast, was contained after overnight rain.
Nineteen homes were destroyed and 14 others sustained some damage in the fire sparked in the seaside community on Thursday.
More than 120 smaller structures and electricity transmissions were also damaged.
The Bureau of Meteorology has issued a severe weather warning for the east of the island, with damaging wind gusts of about 100 km/h expected to continue on Monday.
About 30 firefighters remain on the fireground working on extinguishing hotspots.
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