Three nurses and a patient were injured when a woman attacked them with a pair of scissors at Sydney's Royal Prince Alfred Hospital on Saturday night.

Police say a nurse caring for a patient called for help when the woman, who was also being treated at the hospital, became agitated shortly before 8.30pm.

Two colleagues rushed to help before the female patient grabbed hold of one of the nurses and took her scissors. The woman slashed the arms of two of the nurses and wounded another nurse's back.

She then went into another room where she assaulted another patient.

Doctors, nurses and security staff restrained the woman until police arrived.

She remains under police guard at the hospital. No charges have been laid.

Police continue to investigate.