The police took evasive action and returned the gunfire.
When the shooting subsided, three unidentified men were found suffering from gunshot wounds.
The injured men were taken to the Cornwall Regional Hospital, where they were pronounced dead on arrival.
One black Beretta 9mm pistol, bearing serial number BER020732Z, with a magazine containing one 9mm cartridge; and one black 9mm pistol with the make and serial number erased, loaded with a magazine containing one 9mm cartridge, were seized.
Investigators from the Independent Commission of Investigation (INDECOM) are probing the incident.