1
He is such nice person!
He is such a nice person!
Use such a/an before an adjective + singular countable noun: ‘such a nice person’, ‘such an interesting book’.
2
I can’t believe they can live in such a poverty.
I can’t believe they can live in such poverty.
Use such without a/an before an uncountable or plural noun: ‘such poverty’, ‘such patience’, ‘such nice people’.
Check our grammar lesson on so, such and such a/an.
See SO