The helicopter carrying Pinera, 74, and three others plunged into a lake in southern Chile.
The former president was pronounced dead shortly after rescue personnel arrived at the scene.
The other three passengers survived.
Two sources told Reuters Pinera was the pilot, although officials have not confirmed that, nor the helicopter's intended destination.
President Gabriel Boric declared three days of national mourning, while preparations have begun for a state funeral on Friday for the former leader, who served two non-consecutive terms between 2010 and 2022.
MP/PR