Transcript for Australia fires burn through 15 million acres of land, kill at least 25 people
Reporter: We drive into an inferno. We're struggling to get north right now, hitting roadblock after roadblock. These flames go all the way up and down this highway. It's not just here, it is for miles and miles. A countryside consumed by the wind and heat and flames are really starting to take off. You can hear everything burning behind you. That smoke coming off singing the eyes. For weeks this has been the reality for the people of Australia. Oh my god, oh my god. Apocalyptic, this is the middle of the day. Holy . All of my possessions have been totally incinerated. Reporter: All around the country, homes destroyed by the hundreds. Go, go! Reporter: People evacuating by the thousands. Australia's prone to yearly outbreaks, but changing winds, prolonged drought, and record heat have exacerbated the danger, creating a maelstrom engulfing the country in a ring of fire. They are spreading through ranches and even the edges of town at hugely quick rates. Reporter: Destroying more than 15 million acres of land. At least 25 people have lost their lives. This is just the beginning of their fire season. So we can anticipate even worse impacts in the next weeks. Reporter: To put this into context in 2018's massive California fires, nearly 2 million acres of land were left to ash. The ones in the Amazon, even bigger. But since September, the fires here in Australia have already burned more than three times those events combined. For scale, if you superimpose Australia over the united States, the fire would spread from California to Pennsylvania. Now more than 4,500 firefighters and support personnel are trying to bring this to an end, including 77 from America, 21 more arriving today. Firefighters like volunteer Steve price from Boise, Idaho. It's the biggest fire I've ever been on in my life, and I've been doing it 32 years now. Reporter: In the last week, authorities evacuating residents and tourists as fires intensify. In the face of it, some deciding to stay. Oh my! Reporter: 19-year-old India McDonald, surrounded by the inferno with only a garden hose to beat back the flames. I can't breathe! Reporter: She told Australia's news 9 that against insurmountable orders, she and her firefighter father were able to save their house. On Friday we met Paula and David Durant. They decided to stay behind and fight the flames at their ranch. We're just hoping that, you know, we can save the house if nothing else. Reporter: We weren't to check on them after Saturday's fires tore through. The road to their house was charred with some parts still burning. What was it like here? Oh, horrific. Horrific. Yesterday was really terrible. Really bad. I mean -- the heat, no power. We've got limited phone reception. So we sort of, you know, basically can get a few quick messages out to people. Oh wow, they're still smoking up there. Yeah, and all the way through here and all the way up there in the hills. We're just putting it out. The seems to have hopefully gone around us a little bit more. Reporter: The coastal town of mallacoota, 4,000 residents and tourists were forced to shelter on beaches. Others taking refuge in boats. Some prepared to jump into the water. The sky dark with smoke as fierce winds pushed flames towards them. The evacuation of so many is nearly impossible because of the clouds of dense smoke. The military having to use boats to deliver supplies while they wait. When we were in there, in the thick of it, we thought, this could be it. Reporter: The flames so perilous, these firefighters in south Wales were forced to shelter inside their truck, leaving through a raging inferno. It had got to a point where it was too dangerous to remain in the vehicle. Reporter: A warning to viewers, many of these images are disturbing. Nearly 500 million animals are estimated killed. One Facebook user posting this haunting video of a sea of animals lying dead on the side of the road. As fires ravage much of Australia's fragile ecosystem, the Australia zoo, owned by the late Steve Irwin's family, posting on Instagram they've taken in over 90,000 animal patients. It's scary when you think of how many are lost and there's still so much you can learn from them. We have lost thousands. Thousands of koalas, thousands of so many other species. It's just criminal. This is -- this is the worst event this country's ever seen, without a doubt. Horrific. Reporter: Shane Flanagan is the director at the koala hospital in new south Wales. You see he's burned there. But they've all healed. That was all red, raw. And it's all going nicely now. Reporter: Her hospital is a safe haven for koalas, taking in dozens of animals that have been burned or lost their hab bat, koalas like Paul. Paul went viral after being saved in November at a nature reserve. He was named after the human who rescued him. Hi, Paul. See how he's lost teeth? All the fur's growing back. Reporter: Paul is one of the lucky ones. It's not just burns that are dangerous to koalas, their environment is being destroyed. The fires and the hot, dry air also make them more susceptible to diseases that could render female koalas infertile. This disease with a lot of these burned animals is going to take ought a lot more burnt koalas that have survived the fires, it will kill them. Yeah. And with the drought, there's no moisture out there in the eucalyptus leaves, there's no groundwater, so they're all dying of dehydration, burns, and disease. Reporter: Despite these dangers she says are created by a changing climate, she's determined to protect the species. Up until when these fires happened, I'd never have thought that would be a possibility. But we have another few seasons like this the next few Summers? Heaven help the populations out there. And I say, shame, Australia. Shame. Reporter: Unfortunately, fires approaching this scale are not just an Australian problem. I can't even see, let's get the hell out of here. Reporter: Over the past few years wildfires have become a global catastrophe, increasing in frequency, size, and severity, from Greece to Portugal to the California coast left barren by devastating We are spewing pollution and carbon dioxide into the the science is pretty clear, that that has impacted our climate in a way to cause extreme conditions. You think it's a warning call for Americans? Yes. We've got to change the way we live. You know, we've got to stop being such big consumers and change it. The time is happening now. Mother Earth is getting cranky. Reporter: Cranky, yes. But for those staying behind fighting for their home, it's their only hope. We're not going to go anywhere because we've been lucky. That's all we can hope is that, you know, it's not coming back. They just keep saying, be prepared, be prepared. Reporter: A brief break in the weather offering a little relief and some towns are opening back up, but those monster fires are still raging. With more potential he catastrophic conditions expected later this week, the people here say they're living in constant fear. For "Nightline," I'm Maggie Rulli in new south Wales, Australia.
This transcript has been automatically generated and may not be 100% accurate.