Police in Belgium say they are taking seriously a possible sighting of a girl fitting the description of missing Madeleine McCann.
Detectives have issued a sketch of a Dutch man and an English woman seen with the girl in a restaurant in Tongeren on the Dutch border.
The news comes exactly three months since the four-year-old was abducted from a holiday complex in the Algarve.
A Belgian police spokeswoman said the witness was "trusted" and "100% sure" the girl she saw was Madeleine.
"She works with children and noticed something unusual, that is why we are taking it seriously," the spokeswoman added.
"She said the woman spoke English and the man was Dutch. She said they were acting strangely, but I don't know why."
Checks were also being carried out on the number plate from the couple's car, a Volvo station wagon, the spokeswoman said.
The news follows a number of other reported sightings across Europe of a child resembling Madeleine since she disappeared in May.
Student Jolien Houbrech, 21, who works as waitress at the east Belgian town's De Pauze restaurant said she had served the couple and the girl on Saturday.
Police had removed the girl's drink and taken it away for forensic tests, she said.
She described the child as aged five or six with long blonde hair.
Miss Houbrech said she did not have suspicions about the couple until another customer had alerted her to the girl's resemblance to Madeleine.
"She said that because of her work as a child therapist she had noticed that the people's behaviour was not that of normal parents," Miss Houbrech said.
"After she said that, I said maybe she should call it in to the police."
The couple left before the customer raised her concerns, Miss Houbrech added.
Police said results from DNA tests on the drinks bottle removed from the restaurant were expected next week.