It happened around 12:30 p.m. on South 7th Street in Newark.
Authorities said the retired East Orange police officer interrupted a robbery in progress in front of 35 S. 7th Street.
When confronted by one of the armed suspects the retired officer fired at the suspects.
Two suspects fled on foot while the third fled the scene in the officer's SUV.
Investigators have not determined whether there was an exchange of gunfire, nor if any of the suspects were struck.
The three suspects remain at large.
The retired officer was not injured, officials said. His name was not released.