"It was pretty horrific."
Lambert says the staff were hit, kicked and had things thrown at them. His own staff were hit by the remnants of broken glass, but avoided injury.
"I'm just devastated for my staff. They were just here to cause havoc," he said of the alleged offenders.
He said some of the group had been asked to leave the day before after allegations of theft, but had clearly gone out and gathered more people before returning to attack the store.
To ensure the safety of his staff, Lambert will close his store earlier to ensure they don't have to stay behind after he has left.
"I start at 5am and 4pm is usually my limit of being here. Typically, we're open until 8pm and because I can't be here, I don't think it's fair to leave my staff here.
"I've got to keep my staff safe in any way I can."
Police say they were called to the incident at around 4.45pm, where a number of the youths involved ran away.
A spokesperson for police told the Herald they are concerned about the incident, and are making further inquiries to identify those involved.
"One girl was taken into custody at the scene and has been referred to Youth Aid.
"Another girl was later identified and arrested for assault, trespassing and shoplifting and is due to appear in Palmerston North Youth Court today."
As a result, police will have an increased presence in the CBD area, including around the shopping complex, to alleviate any concerns the public may have following this incident.