@Carolyn584
It would probably be best to contact airbnb customer support.
They are well aware of the Australian bushfire emergency and will definitely assist you to cancel with a full refund, including all service fees.
Here is a snippet of information that airbnb recently sent to hosts
"Bookings in bushfire zones are eligible for refunds under Airbnb's extenuating circumstances policy. If you have been impacted by the bushfires, have a concern around a cancellation, or have any questions, including about how to best communicate, we encourage you to contact Airbnb for support."
Supposedly hosts are able to cancel bookings without penalty during this time, but it is almost certainly safer to make direct contact with customer support. +61 2 8520 3333 . Airbnb is full of glitches and I can see either you or the host ( or both) being penalised for hitting the cancel button.
Best to get airbnb themselves to do so. I'm sure you will find them very supportive.
Regards