The second fatal victim is an occupant of the vehicle.
The accident occurred at 11:55am, in the town of Candemil, on a viaduct towards Amarante-Vila Real, according to local firefighters.
The president of the Junta de Candemil, in Amarante, where the road accident that caused two deaths occurred, told Lusa that the fire engine where the victims were following fell from an "very high" A4 overpass.
According to Ana Sofia Briga, the wreckage of the vehicle is in an area of ??difficult access, with a lot of trees and without houses, on the west slope of the Serra do Marão.
The Candemil viaduct is dozens of metres high and is one of the works of art on the section of the highway that connects Amarante to Vila Real, in the heart of the Serra do Marão.
According to the Amarante firefighters, the fatal victims are a 60-year-old firefighter from Bragança corporation who was driving the vehicle and a 68-year-old occupant of the vehicle.
At 14:15 the traffic was conditioned in the accident area, according to the Porto District Emergency Operations Command (CDOS).