A man posing as a police officer has made a series of attempts to abduct schoolgirls.
On Monday and Tuesday morning four girls between the ages of 11 and 14 were approached by the man, who was wearing normal clothes but tried to convince them he was a police officer.
Children in Hornsey, north London, are being warned to get away as quickly as possible if they are approached by someone claiming to be an officer but who has no identification.
Chief Inspector Jude Beehag-Fisher said: "It would be unusual for police officers in plain clothes not to identify themselves by showing a warrant card, and members of the public are entitled to ask to see one.
"Any child approached by someone in the street in similar circumstances to these incidents, that are not shown any identification that the person is a police officer, should get away from them as quickly as possible, they should shout for help and make sure they tell a parent, teacher or other person in authority as soon as possible. In an emergency always dial 999."
Three girls were approached between 7.50am and 9am on Monday, and another just before 8am on Tuesday. None of them were hurt.
A statement from Scotland Yard said: "At this early stage of our inquiries the allegations are being treated as attempted abductions."
Extra police patrols are being carried out in the area and officers have spoken to local schools.
The suspect is aged between 20 and 30, black, has short, dark hair and was wearing a jacket with the hood up.
A Haringey Council spokesman said: "Incidents of this nature are rare in Haringey, though we fully understand the concern this has caused for parents.
"Pupil safeguarding is a priority for the council and for all local schools and there is a clear focus on ensuring all pupils are aware of 'stranger danger'.
"We are of course supporting the police in their investigation."