Severe thunderstorms and lightning are anticipated across New South Wales, raising alarms about worsening fire conditions amid persistent high temperatures along the east coast.

In response to the extreme fire danger levels on December 27, total fire bans have been implemented in north-west NSW, the greater Hunter, and greater Sydney regions.

Firefighters are currently engaged in battling a significant bushfire in Victoria's Grampians National Park, which has scorched approximately 74,000 hectares, an area comparable to Singapore.

The fire's perimeter extends over 360 kilometers, and the combination of challenging terrain and dry weather is expected to prolong the blaze into the new year.

Authorities are urging residents to stay cool and hydrated while limiting sun exposure due to the high fire danger.

Sydney is forecast to reach maximum temperatures of 38°C today, marking the last day above 30°C until 2025.

While most inland towns will continue to experience high temperatures until the new year, Sydney is expected to enjoy cooler weather over the weekend and into New Year's Eve.

Meanwhile, parts of Queensland are under a low-intensity heatwave warning, with some areas facing severe heatwave conditions.

Brisbane's temperatures are predicted to rise to 37°C on December 28, accompanied by showers expected until the following Thursday.

In contrast, Melbourne is experiencing a temperature drop, with maximums projected to remain below 30°C for the upcoming week.

Hobart is set to have a cooler end to the year, with temperatures expected to stay under 25°C.

The Bureau of Meteorology has warned that thunderstorms may bring little rainfall but could ignite new fires, exacerbating the already dangerous conditions.