For the first time in history, thousands of Defence Force reservists will be deployed to bushfire crisis zones across Australia

Authorities have announced that two people are dead after bushfires tore through large chunks of Kangaroo Island off South Australia.

And the full scale of devastation the island has faced is shown in these horrifying before-and-after photos of the world-famous Southern Ocean Lodge:

South Australian Premier Steven Marshall said there were no details on the identities of the victims but that forensic police are on their way to the scene.

"Very sad that we have heard people have heard that two people have died in the fires," Mr Marshall told reporters.

"The forensic team from SAPOL is on its way, as we have more information we will make it known, at the moment the focus is on informing next of kin, our hearts go out to the family of those people that have been affected."

The hundreds of people gathered at the Kingscote community meeting have stood for a minute silence to mark the two tragic deaths during the #KangarooIslandFires @abcadelaide pic.twitter.com/ngoS4V9mnu — Claire Campbell (@clairehcampbell) January 4, 2020

Mr Marshall continued: "Again, it really does reiterate the very important message that people listen to the alerts, which are coming out now from the CFS. This is a very dangerous situation on Kangaroo Island, and please stay alert to what is going on on the island, and avail instructions from SAPOL."

Daylight has revealed the extent of devastation on Australia's third-largest, with a massive bushfire tearing through some 150,000 hectares of land on Friday.

The iconic Southern Ocean Lodge, a luxury accommodation resort that has regularly been described as one of the world's best, has been totally destroyed.

Operators James and Hayley Baillie told The Advertiser that initial plans were already at hand to rebuild.

“We are absolutely shocked and saddened by today’s events,” Mr and Mrs Baillie told the newspaper.“A bushfire incident such as this is really our worst nightmare come true.”

The luxury Southern Ocean Lodge on KI is destroyed from the bushfire ravaging the island, these pictures captured by the news chopper. Just heartbreaking. More @9NewsAdel pic.twitter.com/ubnBkEphJ4 — Sam Okely (@samokely) January 4, 2020

Most emergency level fires on Australia's third-largest island, a tourism and conservation hotspot off the coast of South Australia, have eased overnight but one on the western half remains uncontrolled.

There are unconfirmed reports of many homes and other buildings, including tourism accommodation, being destroyed after the fire burnt first through Flinders Chase National Park and then east towards the towns of Parndana and Vivonne Bay.

Fires through Friday had burned through "more or less half" of land, according to Mayor Michael Pengilly.

"The destruction is immense," Mr Pengilly told ABC News this morning.

He said there will be large losses of livestock and property but people on the island are understood to be safe.

"To the best of my knowledge everyone got out last night," Mr Pengilly said. "Today is an assessment day to work out where we're at."

Tourism on the western half of the island is expected to take a significant hit. Holiday parks and visitor centres were evacuated into Friday night and while the extent of damage to infrastructure isn't known, Mr Pengilly is worried about what will be revealed.

"To have an island more or less half burnt is unbelievable."

The South Australian Country Fire Service (CFS) issued an extreme fire danger warning early Saturday morning for the Ravine fire on the western end of Kangaroo Island, which said the fire "increased considerably" yesterday.

The fires are at a Watch and Act message.

Mr Pengilly said conditions were mild on the island this morning and there was even some light rain, but the CFS warns the fire remains a threat as the conditions are continually changing.

Local MP Leon Bignell said it had been a long night for those on the island, with people camped out on the Kingscote Oval and others taking shelter in a school gymnasium. He said locals who fled the fire would be looking for information from authorities on when they might return to their properties.

“People over here are in shock, they’re scared, they’re frightened,” Mr Bignell told ABC radio.

The Country Fire Service urged people to defer all non-essential travel to Kangaroo Island. Ferry services to Kangaroo Island will operate as scheduled today, but priority will be given to fire vehicles and personnel.

Kangaroo Island Mayor Michael Pengilly said part of the island looked like it had been hit by a "nuclear bomb".

"It has been absolutely devastating," Mr Pengilly told the ABC, "... the north coast looks like it has been hit by a nuclear bomb."

"Flinders Chase is going to come out of this badly. You can't stop this thing at the moment, it's bloody impossible."

Reminder: Fire Ban and Fire Danger Rating Advice for Saturday 4 January 2020

TOTAL FIRE BAN - KANGAROO ISLAND

Despite a forecast Fire Danger Rating of Very High, SA Country Fire Service (CFS) has declared a Total Fire Ban for Kangaroo Island today. pic.twitter.com/UD5I06eC1y — Country Fire Service (@CFSAlerts) January 3, 2020

Mainland SA was experiencing smoke and dust over the metropolitan Adelaide and other areas on Friday, with the Department of Health expecting the reduced air quality to persist for the next 24 hours.

Chief Public Health Officer Nicola Spurrier said people with chest or heart conditions were urged to stay indoors and follow their personal health management plans.

“We know that exposure to high levels of smoke and dust can aggravate conditions such as asthma, emphysema, bronchitis and other respiratory diseases,” Professor Spurrier said.

“We also know that high levels of dust can be associated with an increased risk of cardiac events such as heart attacks.”

It comes as Victoria and New South Wales brace for a day of hell, with catastrophic conditions set to hit.