North-eastern China's mountainous region (5)
I believe the answer is:
nepal
'mountainous region' is the definition.
(mountainous country in Asia)
'north-eastern china's' is the wordplay.
'north eastern' becomes 'NE' (abbreviation).
'china' becomes 'pal' (china plate is Cockney rhyming slang for mate).
'ne'+'pal'='NEPAL'
(Other definitions for nepal that I've seen before include "somewhere in the Himalayas" , "mountainous area" , "Hindu kingdom in south Asia" , "Country in plane north-west of India" , "World's only Hindu kingdom" .)