A man has died after police were called to a fourth Sydney stabbing in 24 hours.

Police say three youths are in custody after a man was found seriously wounded at the Parramatta Station bus interchange on Fitzwilliam Street about 5am.

The 20-year-old victim was taken to Westmead Hospital in cardiac arrest, where he later died.

The trio aged 16, 17 and 19 were arrested at nearby Hassall Street, and have been taken to Parramatta Police Station where they are assisting with inquiries.

No charges have yet been laid.