McDonald's has launched an investigation to try to figure out how much glass from a broken lightbulb could have potentially made it into its buns.
The fast-food giant shut about 50 of its 24/7 North Island outlets between about midnight and 3am on Saturday after a broken lightbulb was noticed on the floor next to the production line that makes the buns in the North Shore, McDonald's spokesman Simon Kenny said.
Suppliers said it was an extremely low risk, but could not guarantee the buns were glass-free.
Late on Friday night management made the decision to pull all buns from its restaurants which could have been contaminated.
That meant closing the stores, and then using the breakfast menu until restaurants were supplied with new buns.
The last restaurant to receive a new supply was Gisborne, yesterdayafternoon, Mr Kenny said.
An investigation was launched on Friday night.
"What they try and do is put the light bulb back together, all the broken pieces of glass and see what's left over.
"What they don't know, that's what they're trying to work out now, is what percentage of glass could be missing and if it was missing, and it's not on the floor, what could have happened."
It was not known when the lightbulb smashed, but it could have happened as long as a week ago since the room had not been checked since last Sunday.
"... We felt there was probably a couple of days worth of potential that the buns could have been in the restaurants [with glass in them]."
McDonald's had not yet received any complaints from its customers.