“The guard had a quarrel with another security guard while on duty on Friday,” Warrant Officer Kay Makhubela said.
“The other one took out a knife and stabbed him. He was rushed to the casualty ward where he died.”
Both guards worked for the hospital.
Makhubela said the perpetrator fled the scene after the incident.
“He went on the run, and he has not been arrested yet.”
The National Education, Health and Allied Workers Union (Nehawu) said the incident had happened after it had held a service delivery protest there earlier on Friday.
“Nehawu is shocked by the news,” spokesman Sizwe Pamla said in a statement.
“We send our deepest condolences to the family of the deceased security guard and call on the law enforcement agencies to arrest and prosecute the perpetrator.”
Nehawu members protested outside the hospital over several issues including poor hospital security.