"Everything seems to indicate that the fall happened when they were probably trying to take a selfie," Rui Pereira da Terra, head of the rescue service in Cascais port near Lisbon, told AFP.
"It seems they dropped their mobile phone and fell down while leaning over to retrieve it," he added.
The fatal accident happened in the coastal town of Ericeira, a popular surfing spot 30 kilometres (18 miles) from the Portuguese capital.
The beach is ringed by cliffs and a 40-metre high wall.
It was not the first time that tourists had fallen off the wall.
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