A doctor visiting South Australia and somewhere in the Pacific (5)
I believe the answer is:
samoa
'somewhere in the pacific' is the definition.
(Samoa is a nation in the Pacific Ocean)
'a doctor visiting south australia' is the wordplay.
'doctor' becomes 'mo' (medical officer).
'visiting' is an insertion indicator.
'south' becomes 'S' (abbreviation).
'australia' becomes 'A' (abbreviation for Australia).
'a'+'mo'='amo'
's'+'a'='sa'
'amo' inserted into 'sa' is 'SAMOA'.
'and' is the link.
(Other definitions for samoa that I've seen before include "South-west Pacific nation" , "Polynesian island group" , "Pacific island nation, capital Apia" , "Group of volcanic islands in the S Pacific" , "Polynesian isle" .)