Conditions in the nation's bushfires are worsening with fire tornados spotted and nearly half a billion wildlife impacted.

Experts are worried that fires burning out of control in two states could come together later this week to form a mega fire with its own weather system.

The bushfires, currently burning on either side of the NSW border with Victoria, have torn across large swathes of land and are showing no signs of slowing down despite cooler conditions and some rain.

As of this morning, there’s only about 10km of space that stands between Victoria’s Corryong blaze and two others that are burning at Kosciuszko National Park in NSW.

The fires are so intense and so hot that fighting them directly is not an option for firefighters — instead they hope to contain them and save properties in townships on the outskirts of the fire.

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Right now the fires are burning separately, but high temperatures are returning later this week and the threat of a mega fire is looming.

“It’s very concerning,” Victoria’s State Response Controller David Bruce said this morning.

“Obviously we have some conditions on Thursday and Friday which will increase the fire danger ratings and, with the potential of these fires joining up, will create some weather conditions that will be very unpredictable and very challenging to fight.”

Those conditions include scorching temperatures in the high 30s for Corryong on Thursday and on Friday where more than 150,000 hectares of land has already been scorched.

Emergency Management Commissioner Andrew Crisp said the “potential spike days” mean those in regions already affected by fire or in the path of moving fires need to be vigilant.

“This will be a changing, dynamic situation,” he said. “We know that the weather will start to warm up (later this week).”

As bushfire experts do their best to predict the movement of unpredictable fires, authorities are being hampered in their efforts to establish exactly how much land has been affected and whether several different fires have merged.

“Unfortunately, one of the challenged with (analysing fires from above) where it’s either cloudy or a lot of smoke (is that it) makes it difficult to get a picture,” Emergency Management Victoria’s state control centre spokesman Luke Hegarty told The Age.

“We’re still very actively trying to prevent (a merge between fires at Corryong and Tumbarumba in NSW) from happening but we recognise we didn’t have crews on fire line … due to the dangers with that.”

What authorities can say with some certainty is that more than a million hectares have burnt statewide in Victoria and of those, more than 800,000 are in the East Gippsland area.

In NSW, there are 136 fires still burning, with more than 69 uncontained, including a massive blaze southwest of Eden on the far south coast, which has torn across more than 140,000 hectares.

As the fires on either side of the NSW and Victoria border threaten to come together, authorities are voicing concerns about difficulties in controlling the movement of people. Or, more specifically, the lack of movement.

Fire authorities fear high temperatures and strong winds could merge three fires across New South Wales and Victoria into one 'mega blaze'. #9Today pic.twitter.com/J1TDoC23pW — The Today Show (@TheTodayShow) January 5, 2020

Incident Controller Leith McKenzie told reporters she was “very frustrated” that up to half of all residents living between the two blazes had decided to stay where they are.

“They’re stubborn and they don’t want to move,” she said. “They’re defending their life and that’s what they know.”

Seven people have so far been killed in fires in NSW. Another two people died in fires in Victoria and more people are missing.

The Victorian government has announced a dedicated fund to support Victorian bushfires survivors, contributing $2 million.

Australian comedian Celeste Barber helped raise a staggering $30 million by Sunday evening to help NSW firefighters.