Number increases in emergencies (6)
I believe the answer is:
crises
'emergencies' is the definition.
(I've seen this in another clue)
'number increases' is the wordplay.
'number' becomes 'c' (C is an example).
'increases' becomes 'rises' (rise is a kind of increase).
'c'+'rises'='CRISES'
'in' acts as a link.
(Other definitions for crises that I've seen before include "serious problems" , "Catastrophes" , "lot of emergencies" , "moments of disaster" , "Times of great danger" .)