"Everything seems to indicate that the fall happened when they were probably trying to take a selfie", Captain Rui Pereira da Terra of the nearby Cascais Port rescue service said.
A beach cleaner found their bodies on Tuesday morning at Pescadores beach in Ericeira, 30km from Lisbon.
It was unclear which of the pair is an Australian citizen.
"It seems they dropped their mobile phone and fell down while leaning over to retrieve it", he added.
One Portuguese newspaper reported that fishermen discovered the couple's bodies at about 6.30am.
"Only when they got closer did they realise it was a dead couple and they were shocked with what they saw".
The report did not name the couple but said the woman was 30 and the man 40, although other reports gave slightly different ages.
Michael Kearns, 33, and his 37-year-old partner Louise Benson are believed to have died early on Tuesday local time after falling from a cliff in the popular tourist town of Ericeira, about 35 kilometres north of Lisbon.
According to AFP, it is not the first time tourists have fallen from the high stone wall.
Meanwhile, the British Foreign and Commonwealth Office has stated that it was in touch with local authorities "following the death of a British woman in Portugal and stand ready to provide support to her family".
The beach at Pescadores is surrounded by cliffs and a 30-metre high wall covered in shrubs.
The Foreign Office confirmed a British woman had died and the Australian Department of Foreign Affairs (DFAT) and Trade said an Australian had lost their life.
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Celebrities Who Suffer With Chronic Diseases
Now if that isn’t the epitome of what a BFF is, I don’t know what is! Selena continues to be on chronic medication. There is also a huge list of celebrities past like famous painter vincent Van Gogh who suffered with this disease.