Large area up in Kerala is ablaze (4)
I believe the answer is:
asia
'large area' is the definition.
(I've seen this before)
'up in kerala is ablaze' is the wordplay.
'up' says the letters should be written in reverse (in down clue: letters go upwards).
'in' indicates a hidden word.
'aisa' is hidden in the letters of 'kerala is ablaze'.
'aisa' reversed gives 'ASIA'.
(Other definitions for asia that I've seen before include "its pampered jades couldn't draw much?" , "huge region" , "Major land mass" , "Thailand and its location" , "A vast number of people have lived here" .)