Ecologists at the University of Sydney are estimating that nearly half a billion animals have been killed in Australia's unprecedented and catastrophic wildfires, which have sparked a continent-wide crisis and forced tens of thousands of people to flee their homes in desperation.

How did Australia fires start and what is being done? A very simple guide.

Australia is fighting one of its worst bushfire seasons, fuelled by record-breaking temperatures and months of severe drought.

Since September, at least 25 people have died and thousands have been made homeless.

Here's a very simple guide to what's going on: