Vast region back in Australia is ablaze (4)
I believe the answer is:
asia
'vast region' is the definition.
'Asia' can be an answer for 'region' (Asia is a continent). I am unsure of the 'vast' bit.
'back in australia is ablaze' is the wordplay.
'back' is a reversal indicator.
'in' indicates a hidden word.
'aisa' is hidden in the letters of 'australia is ablaze'.
'aisa' written backwards gives 'ASIA'.
Can you help me to learn more?
(Other definitions for asia that I've seen before include "Major land mass" , "its pampered jades couldn't draw much?" , "One-third of all land" , "Continent in which India is situated" , "The nations of the East, collectively" .)