The incident reportedly took place incident outside Reid’s Pharmacy, New Street at about 15:30 on Saturday 18 March 2023.
Officers said: “A male, described as white, wearing a black jacket, black trousers, a baseball cap and carrying a rucksack has walked into a nearby building site at the junction with New Street and Vauxhall Street, without permission.
“When challenged on leaving the building site this male has produced a small knife and made threats to workers before making off towards Devonshire Place. No person was injured as a result of this altercation.
“Anyone who may have seen this or who has any information is asked to contact police on 612612 or the independent charity Crimestoppers anonymously on 0800 555 111 or via their Anonymous Online Form at Crimestoppers-uk.org.”