A firefighter has died on the New South Wales mid-north coast, as the state’s premier issued a warning about a “foreboding beginning” to the bushfire season.

The deputy secretary of the NSW National Parks and Wildlife Service, Alex Graham, on Monday confirmed the death of one of their firefighters.

“At approximately 11pm Sunday, the firefighter was struck by a tree while working on a bushfire at Bulahdelah on the state’s mid-north coast,” Graham said in a statement.

“Fellow firefighters provided first aid until NSW Ambulance paramedics arrived at the scene. Our thoughts are with the firefighter’s family during this difficult time.”

The premier, Chris Minns, said it was “obviously a terrible reminder of how difficult and dangerous this work is and how the people who put their lives on the line to protect lives and property do an incredible job”.

“It’s a deeply distressing turn of events, and a sad day for NSW this morning,” Minns told ABC TV.

There were about 700 firefighters across NSW working on Monday morning to contain blazes, including nine that remained uncontained.

Minns said it was “quite a foreboding beginning to the bushfire season”, being only a couple of days into summer.

Jihad Dib, the NSW emergency services minister, said the death was a reminder of the dangers that firefighters face.

“These are people who put themselves in harm’s way to protect the community, and this particular person has made the ultimate sacrifice,” he said. “It’s a very, very sad day for all of us.”

On Sunday, the NSW Rural Fire Service said 16 houses had been destroyed in a fire in Koolewong, not far from built-up areas on the Central Coast, with a further nine houses damaged and seven outbuildings destroyed.

Another four homes were lost at Bulahdelah.

Storms and damaging winds would keep fire danger high across parts of Australia, with authorities calling for vigilance after a weekend of significant losses.

On Sunday, Minns said December was shaping up as a particularly tough period for fire danger, owing to westerly winds and warmer waters off the Pacific Ocean.

“Unfortunately, we’re likely to have more volatile weather periods in the years ahead due to the changing climate,” the premier said.

With easing conditions across NSW, firefighters supported by aircraft were continuing to strengthen containment lines. But authorities urged the community to stay vigilant.

Federal and state disaster assistance funding has been activated across the Central Coast, mid coast, Upper Hunter, Muswellbrook, Warrumbungle and Dubbo regions.

More than 250 firefighters, 50 trucks and nine aircraft battled the Koolewong blaze at its peak.

In Tasmania, authorities confirmed a 700-hectare blaze at Dolphin Sands, near the Freycinet national park on the state’s east coast, was contained after overnight rain.

Nineteen homes were destroyed and 14 others damaged in the fire that was sparked in the seaside community on Thursday.

More than 120 structures were damaged, including sheds, caravans, water tanks, carports, garages and electricity transmissions.

“With increasing winds and debris still present on properties, conditions pose safety risks to the community,” Tasmania’s fire and emergency services commissioner, Jeremy Smith, said.

Australia’s national annual average temperature is about 1.5C higher than in 1910, according to the Bureau of Meteorology, and the climate crisis has increased the frequency and severity of extreme weather events.