A 25-year-old man has died after paramedics say an angry crowd prevented them from treating him in Sydney’s south.

Paramedics were called to Iris Avenue in Riverwood where the man was suspected of having suffered an overdose on Sunday morning.

Five paramedics arrived but were not able to treat the man, who they said was in cardiac arrest.

The Australian Paramedics Association (APA) said relatives of the man became "irate" and a crowd of "angry males" tried to intervene, blocking those trying to treat him.