Police Scotland has activated the national Child Rescue Alert system to help them trace a three-year-old boy missing in Edinburgh.
People in the city have been asked to look out for Mikaeel Kular.
He was last seen going to bed in Ferry Gait Crescent at about 21:00 on Wednesday, but when his family woke he was not in the house.
Supt Liz McAinsh said there have been no sightings of Mikaeel since then.
The Child Rescue Alert system means calls to its 0300 200 0200 number will be answered by dedicated members of staff.
Police said they are seeking information from anyone who has seen Mikaeel or anyone matching his description in the past 24 hours.
They said there was no evidence to suggest criminality at the moment, but officers were "keeping an open mind."
Mikaeel is 3ft tall and was possibly wearing a beige hooded jacket with grey fur-lined hood.
He may also have had on black gloves with multi-coloured fingers, dark navy blue jogging bottoms, a grey pyjama top featuring an embroidered turquoise dinosaur on the chest and brown Clark shoes with two Velcro straps.
He has a faded scar on the bridge of his nose and a sore on the left side of his mouth.
Police sources have indicated that an operation in Waterfront Gait, a mile from Mikaeel's home, was not connected with the investigation into the boy's disappearance.
There, officers detained a man as a witness in connection with an "unconnected" inquiry.
Supt McAinsh said the focus of the police operation remained in the local area, and officers were working to narrow down the timescale in which Mikaeel went missing.
She confirmed there had been no sightings of the missing boy, and no signs of a door being left open in the property.
She was not aware of anyone else having access to the flat, she said.
A number of people were helping officers with their inquiries, the officer said, but there were no suspects, and had been no arrests or formal detentions.
She added: "I would stress at the moment we have no indication at all of any criminality. It remains a missing person inquiry.
"Our concern is obviously - with the passage of time - he was last seen at 9 o'clock last night and it's a cold day that we had.
"I would ask people in the locality please continue searching in your own personal property.
"If your neighbours are away, then think about searching their gardens, their sheds, common stairs, wheely bins."
Mikaeel, who is British with Asian parents, was at home with his mother and four siblings, including his twin sister, on Wednesday night.
Officers are speaking to "all family members" about the disappearance.
Coastguard teams and lifeboats have been searching the shoreline in the Cramond and Drylaw area.
Efforts were made to speak to Mikaeel's father, who is understood to be of Pakistani origin.
Supt Liz Ainsh said: "We've spoken to all key members of the family. We've been in contact with them and they are assisting us with our inquiries.
"We have no suspects because we have no evidence of any criminality.
"We haven't had any sightings of Mikaeel and that obviously causes us concern."
Supt McAinsh was asked by reporters if it would have been possible for a three-year-old boy to have got out of his home on his own.
"I have been assured that it is possible," she said. "I would suggest also that anything's possible.
"Three-year-old children are quite resilient and they have quite a great deal of strength and ability to open doors and I'm assured that Mikaeel is capable of doing that."
Temperatures overnight in Edinburgh dropped to 2.3C (36F) by 04:00, according to the Met Office.
The Police Scotland helicopter has been involved in the search operation.
Supt McAinsh said: "He would normally share a bedroom with his twin sister but my understanding is that he was sleeping in the bedroom alone last night."