Police are investigating a "potential sighting" of a child matching the description of missing three-year-old Mikaeel Kular as hundreds of volunteers continue to search for the youngster.
Members of the public reported seeing a boy who was "small in build and alone" in West Pilton Gardens, Edinburgh, at around 8.30am yesterday morning.
Mikaeel disappeared from his home in the Scottish capital after being put to bed on Wednesday night.
Police Scotland have appealed for information and said the young boy spotted was wearing a cap.
However, Superintendent Liz McAinsh said Mikaeel does not usually like wearing something on his head.
The timing of the sighting has been confirmed by CCTV but the footage could not confirm the identity of the child, she said.
She said: "Members of the public have come forward to report seeing a boy walking in the vicinity of West Pilton Gardens at 8.30am yesterday.
"The witnesses were in a vehicle driving down West Pilton Gardens at the time they saw the boy.
"They described seeing a small boy on the right-hand side pavement running towards the junction with West Pilton Park.
"They noticed him because he was small in build and alone at the time. They said he matched the description given of Mikaeel, although they also reported the child they saw was wearing a cap or hat.
"He doesn't like wearing a hat or a cap, is my understanding, and to our knowledge he didn't have one, there's not one missing from the house."
She added: "We would ask that anyone who also saw this child contact us as a matter of urgency.
"We need to confirm if this was Mikaeel or if it was another child. If it is your child who was out at this time and in this location, we want to hear from you so we can eliminate this line of inquiry as swiftly as possible."
Hundreds of people have joined in the search for the missing youngster as police said they are becoming increasingly concerned.
Volunteers standing shoulder to shoulder have been scouring the foreshore at Cramond. Those taking part ranged from firefighters to mothers wheeling prams.
Investigations near and at the family home in Ferry Gait Crescent are continuing.
Several communal bin areas were cordoned off this afternoon.
Four forensic officers in white suits and masks were seen entering the family home.
Officers said earlier they had spoken to Mikaeel's father and all of the boy's family are said to have been very helpful to the police.
The boy's mother has been named locally as Rosdeep Kular, 33.
She is said to be getting support from police, her family and friends, but is "very distraught".
A missing person appeal is to be displayed on digital billboards across the UK, the charity Missing People confirmed.
Yesterday, police detained a man in the city's Waterfront Gait but said it was unconnected with the boy's disappearance.
The Daily Record reported that the detained man lived at the same address as Rosdeep's first husband.
Hundreds of police officers are involved in the searches today and specialist search teams, mounted officers, dogs, other emergency services and local organisations are also involved in the investigation.
Mikaeel's mother put him to bed at around 9pm on Wednesday only to find his room empty when she checked at about 7.15am yesterday.
The little boy, who has two sisters and two brothers, usually sleeps in the same room as his twin sister but was alone on Wednesday night.
His jacket and shoes were missing and police are looking into whether he might have left of his own accord.
He may also be wearing black gloves with multi-coloured fingers, dark navy blue jogging bottoms, a grey pyjama top with an embroidered turquoise dinosaur on the chest and brown Clarks shoes.
Police have activated the UK-wide Child Rescue Alert system, which is usually reserved for abduction and kidnap cases.
Anyone with information relating to the sighting or the boy's disappearance is asked to contact the dedicated telephone number 0300 200 0200.