Police say they will arrest any pranksters taking part in the terrifying "killer clown" craze – after reports the unsettling fad has reached Hertfordshire.

The frightening prank has swept America and has now cropped up in the UK with reports of people dressed in clown masks and costumes scaring unsuspecting victims - usually schoolchildren.

There have been five reported incidents across the county and Hertfordshire Constabulary said they are working to understand the nature of these calls.

No reports of physical threats of harm or violence have been logged with clowns typically frightening people in passing cars or staring at individuals from a distance.

However, the intimidation caused has prompted police to step in.

In a statement today, Chief Inspector Gerry McDonald said: “Although the people dressing up as clowns may think they are taking part in some harmless fun, they should be mindful of the impact their actions may have on others and be aware that any behaviour that causes another person alarm or distress could lead to them being arrested under the Public Order Act 1986.

“We want people to enjoy themselves as we approach Halloween but not at the expense of others."

In one incident a man dressed as a clown was approaching shoppers outside Tesco in Jarman Park, Hemel Hempstead, whilst being filmed by his laughing friends. 

CI McDonald added: “It is also important that people use social media responsibly and do not post items that could further fuel this ‘craze’ and create unnecessary fear within the community.”

“At this stage it is unclear whether some of these reports have been made by hoax callers.

"I’d like to remind the public that the Constabulary will take robust action against anyone who makes hoax calls to the force as this can divert precious resources away from real emergencies.”

Clowns are a common cause of phobia, partly due to the Batman villain Joker and the novel and subsequent film It – the author of which, Stephen King, has called for the craze to end.