Police were reviewing CCTV footage and seeking witnesses, many of whom fled the restaurant.
The dining area and counter were closed as police investigated, while staff dealt with increased traffic at the drive-through.
At least one weapon was recovered. "No, it wasn't a plastic knife," Pritchard said.
The restaurant is staffed mainly by young people, family of whom expressed concern on a Facebook thread, which included parents worried about the traumatic effect on teenagers and children who witnessed the violence.
One commented her daughter had been there, and was so traumatised she didn't want to go back.
"Poor girl," another responded. "She has to live with that. Nobody deserves to see that crap."
It was business as usual at the restaurant today, and the window has been replaced.