The reports of suspicious clowns have led to US schools being shut down, and police forces have warned people to be wary if they see anyone dressed as one.
Many sightings of scary clowns and reports of them frightening people have turned out to be pranks, and police have complained that is leading to a waste of their resources.
Sociologist Robert Bartholomew, who has studied mass hysteria for decades, told Newstalk's Larry Williams the clown fear was referred to as a "social panic".
Social panic involved an exaggerated fear among a large number of people about some evil that was supposedly threatening society.
Dr Bartholomew said clowns were basically good until the 1930s, when a new type of clown appeared in American circus sideshows.
"These were creepy clowns, sadistic, evil..."
In the 1950s and 1960s in America popular television shows for children featured friendly clowns.
Things changed in the 1980s when Hollywood started to make movies about clowns terrorising people, especially children.
"So since about 1980 I've counted 186 films and TV shows depicting bad clowns," said Dr Bartholomew.
There was a pattern regarding the recent clown sightings. Somebody claimed to see something, then there was media coverage, then those in the area started to scrutinise their surroundings.
The fallibility of human perception generated more sightings and copycat hoaxes arose.
Dr Bartholomew said though perception was fallible, police had to take these things seriously, while exercising judgement.
"Every panic has its underlying fear and here I think it has to do with the uncertainties that are going on in the world today. It's part of the greater social panic about the fear of strangers and terrorists and an unpredictable world."
Waikato District Police are urging calm over the clown situation.
In a Facebook post they said people were getting "freaked out" by trolls creating fake Facebook profiles with clown profile pictures.
"To date we haven't locked up any murderous clowns purging towns as they have promised."
They urged users confronted by such a profile to block the user and report the profile so Facebook could delete it.
Anyone who saw a clown in public should relax, but call police if they felt threatened.
"Maybe ask them to juggle or tie a balloon animal to see if they're legit."
A "Clown Lives Matter" march has been organised in America following the creepy sightings.
Professional clowns said they were being unfairly maligned amid the hysteria which has led to several teenagers being criminally charged for making threats against their schools.
More than 100 professional clowns were expected to join the march in Tucson, Arizona on October 15.
The organisers said: "This is a peaceful way to show clowns are not psycho killers. We want the public to feel safe and not be afraid. So come out, bring the family, meet a clown and get a hug!"
