The Cessna plane departed from Dinan, near Rennes in western France. It was bound for Jersey and the victims are thought to be British residents, police said.
The mid-morning crash sparked a major air and sea search operation involving helicopters from France and Britain as well as a British navy vessel that was in the area.
"Following a comprehensive search and rescue mission... We now believe there were no survivors of this morning's light aircraft crash," the police statement said.
Earlier, a spokesman for the Port of Jersey authority told AFP the plane had crashed into the sea about eight kilometres west of Jersey at 10.20 am (1450 IST).
"Some wreckage has been located," he said, adding: "There was a lot of sea fog along the immediate coastal shore this morning, but we don't know if that was the issue.