The police say that the reports include people posting on social media, as well as sightings of people dressed as clowns.

Officers were told that a group of young people aged 12-13 were heard talking about obtaining clown costumes and knives and going to Sainsbury's in Penrith to scare people.

There has been a rise in the number of incidents since September 30, with reports to police of people dressed as clowns to scare people. "Not only could they by committing a public order offence, which will see police action, their actions could cause delays for other emergencies requiring police attendance".

On Sunday, Thames Valley Police said it had been called to 14 incidents in 24 hours.

Another person reported seeing a clown jump out into the middle of the road while they were driving in Chigwell Row, Hainault.

"We believe this to be part of a much larger prank which is now sweeping across the United States of America and parts of the UK. We don't want to spoil the Halloween fun but we do want people to feel comfortable and safe", he said.

Police in other parts of Britain have reported similar cases.

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The spokesman added: "Whilst we do not want to stop people from enjoying themselves it is important that while having fun they keep in mind to act in a responsible manner and understand that they could be prosecuted if a criminal offence is committed".

"Their behavior is causing multiple reports to our call takers and is tying up police resources which could impact on calls to other incidents".

Children are being put off clowns due to the recent "killer clown" craze and this is "frightening" for the industry, a professional party entertainer Mattie The Clown said. Authorities in Australia and Canada have also issued clown-related cautions in the last several days.

It is the latest incident in a weird craze that is causing West Mercia Police increasing concern. They urged those in their community to contact their local station if concerned.

Clowns have apparently been spotted in Maidstone and Paddock Wood. "You may be arrested if you are putting people in fear".

She then warned that people who are into the clown stuff tend to be "dangerous".