A young man has died from stab wounds in a Sydney hospital and another man is in custody.

The 22-year-old, who was dropped off by taxi at the Mt Druitt Hospital just before 5pm on Wednesday, had been stabbed in the body and head. He died despite the efforts of medical staff.

A 56-year-old man was arrested after inquiries at a unit in Tregear, where a crime scene was set up.

The older man was taken to Nepean Hospital under police guard.