An artist's impression was released of a man seen acting suspiciously in the vicinity of the Portuguese holiday complex where Madeleine vanished in May last year.

The sketch was based on a description given by a British holidaymaker, and bears a striking resemblance to an earlier drawing of a man seen carrying a child on the night of Madeleine's disappearance.

The McCanns' official spokesman said it was vitally important the man was traced as soon as possible.

"Who is he? Where is he? What, if any, is his connection to Madeleine's disappearance?" Clarence Mitchell said at a press conference in a London hotel.

"If he is innocent we want him to come forward for his own sake so he can be ruled out.

"We believe this man could be linked to Madeleine's disappearance."

Four-year-old Madeleine vanished from her parents' holiday apartment in the Portuguese resort of Praia da Luz on May 3 last year.