Police say a family saw the man with a blond-haired child of three or four, possibly wearing pyjamas, heading away from the McCanns’ holiday apartment.
Madeleine McCann, from Rothley, Leics, was 3-year-old when she went missing on May 3, 2007, in Praia da Luz, Portugal.
The e-fit images will feature in a BBC Crimewatch appeal later.
The witnesses said the man was white, 20 to 40 years old and of medium build. He had short brown hair, was clean-shaven and of medium height, they added.
Detective Chief Inspector Andy Redwood, the senior Metropolitan Police investigating officer, said he could be the man who took Madeleine but there could be an innocent explanation.
The Met Police opened up a new investigation earlier this year and have been reassessing all the gathered material.
As a result, according to the police, the timeline and “accepted version of events” surrounding Madeleine McCann’s disappearance have significantly changed.
Andy Redwood said he was now attaching more weight to the sighting of the man and the child at 10pm, which was later than the time it was previously believed Madeleine McCann was taken.
Madeleine McCann and her brother and sister were left in the apartment at 8.30 p.m. while her parents dined with friends at a nearby restaurant. Her father, Gerry McCann, checked on them at 9.05 p.m. and her mother, Kate, raised the alarm at 10 p.m.
Andy Redwood said the child in the man’s arms had not been crying, nor looked in distress.
He added: “Whilst this man may or may not be the key to unlocking this investigation, tracing and speaking to him is of vital importance to us.
“This is far from our only line of inquiry and there will be e-fits released of other sightings as well, who we are equally keen to trace.
“These people were seen on the day of Madeleine’s disappearance and the days leading up to it.”
UK’s PM David Cameron said he was “very pleased” Scotland Yard were doing this work, which the government was helping to fund.
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