Centre of Hirosaki, also known as a Japanese port (5)
I believe the answer is:
osaka
'a japanese port' is the definition.
(I've seen this before)
'centre of hirosaki also known as' is the wordplay.
'centre of' means to look at the middle letters.
'also known as' becomes 'a.k.a.' (synonyms).
The middle letters of 'hirosaki' are 'os'.
'os'+'aka'='OSAKA'
(Other definitions for osaka that I've seen before include "S. Japan port, bay" , "Major port and commercial and industrial centre on Honshu" , "Japan's third-largest city" , "Place" , "Japanese metropolis" .)