"Saint Kentigern College wishes to inform that all remaining scheduled performances of Sweeney Todd have been cancelled," the announcement said.
"If you ... have paid by credit card you will automatically be refunded by iTicket early next week.
"We sincerely apologise for any inconvenience this may cause. Naturally this is a trying time for the school, students, and their families.
"We hope you'll join us in sending your thoughts ... to all involved."
The company said all customers affected by the cancellations would be reimbursed in full early next week. Credit card payments would be returned automatically, and people who paid by other means would be contacted individually.
College head Steve Cole said the school was still trying to figure out how the opening night scene went so wrong, after months of rehearsals including eight dress rehearsals.
Toi Whakaari drama school director Christian Penny told the Herald he did not think it was common for schools to use real weapons in their drama productions.
"I would be highly surprised."
A real blade would almost never be used in a professional production at Toi Whakaari due to health and safety requirements, he said.
"This is training for the professional industry. Health and safety is right up there."
Because school productions are run by teachers, who are busy and not trained professionals, health and safety standards are not necessarily enforced in the same way, he said.
"In a high school you've got people doing the best with what they've got.
"It's an amateur culture and these kinds of accidents can happen. It's not good, but it can happen."
Safety guidelines published by Entertainment Technology New Zealand state that all swords, knives and blades used should be blunt.
