Nottingham has been put under a dispersal order after a prank which has been described as potentially "intimidating" took place in the city centre.
Nottinghamshire Police, who received two alerts about large gatherings of pupils, announced the order on Thursday afternoon.
The order was put in place in response to a social media prank involving ties being forcibly removed from pupils from other schools.
Police revealed officers had not received any reports of crimes being committed.
An image of trader Abdelitef
However, parents of pupils across the East Midlands city have received emails warning them about the trend.
A text to parents of Bramcote College pupils warned: "The planned disorder is part of a craze where school aged children assault students from other schools, take their school ties and burn them; all whilst filming and sharing it on social media."
Police presence around Nottingham's Old Market Square is particularly pronounced this evening.
Nottinghamshire Police Chief Inspector Karl Thomas was clear that no offences have been reported.
However, he also confirmed extra patrols would take place.
Detective Inspector Thomas said: “Over the last few days we have been alerted to two large gatherings of school children in and around the city centre.
"We believe this is linked to an internet prank and poses no danger to the public.
"No crimes have been recorded due to these two gatherings.
An image of Nottingham
“However, we realise this can appear intimidating for those visiting the city and have therefore put some measures in place.
"We have increased our patrols in the city and issued a temporary dispersal notice that will allow us to direct people away from the city centre if we believe they are involved in the prank.
“We would encourage school pupils not to carry out the prank which involves removing the school tie of a pupil from a different school and posting it on social media.
"We have also contacted all city schools to ensure the message is sent out to parents and family members so they can be made aware.”
People in Nottingham voiced their concern with the activity on social media and confirmed a larger police presence.
Paul, a trader on Continental Market, told GB News: "There's been a high presence of police this afternoon around the marketplace from what I can see from my stall .
"There's been 10 or 12 extra police wondering around but I haven't seen that many kids, only the normal kids leaving school."
Abdelitef, also a trader, added: "There were some young people here and police were trying to monitor them and make them behave ... I thought something was happening but for the safety and the peace of the public."
He added: "This is not nice to see but I think as long as the police are involved that is good."