A masked man with a painted face and who was carrying a knife jumped out on a group of children and followed them to school in the latest of the so-called "Killer Clown" incidents.
The pupils, aged 11 and 12, were on their way to the Hermitage Academy in Chester-le-Street, County Durham, at 8.40am when they were given the fright - leaving them distressed but unhurt.
The clown was wearing grey tracksuit bottoms, red shoes, a multi-coloured top, a mask and had his face painted.
Neighbourhood Sergeant Mel Sutherland, said: "The children arrived at school understandably upset and distressed by this incident and we are currently trying to locate this man.
"My officers will be on patrol outside the school at home time this afternoon to offer reassurance to children and parents.
"We believe this to be part of a much larger prank which is currently sweeping across the USA and parts of the UK.
"It is very alarming he was carrying a knife - however, we do not think he intended to harm the children and as far as we are aware, this is part of the prank.
"There are currently several social media accounts dedicated to this 'Killer Clown' craze and we are also looking into those and who is using them.
"I would like to appeal directly to the people who are dressing up and carrying out these stupid acts to think seriously about what they are doing, the distress they are causing to young children is unnecessary and it needs to stop."
Earlier this week, Northumbria Police issued an appeal and warning after a series of incidents in Newcastle involving people dressed as clowns jumping out and scaring schoolchildren.
A 13-year-old boy was arrested in the Blakelaw area of the city on Tuesday following reports of someone dressed as a clown attempting to scare passers-by.