A high school production of an infamously gory play became a real-life nightmare when two students were slashed with an actual razor mistakenly used during the opening night’s show.

New Zealand’s Saint Kentigern College on Wednesday was in the middle of its second act of Sweeney Todd when two 16-year-old boys had their necks cut on stage, authorities said.

The teens had been acting in a throat-cutting scene when they were injured with what everyone thought was a prop.

Emergency responders rushed the boys to Auckland hospital, where one was in serious condition and the other was being treated for moderate injuries, according to reports.

“No announcements were made to the audience that the throat slitting was not all just fake blood,” an audience member said, according to The Guardian. “The show went on; we never knew anything about the real blood being split until later.”

Read: Woman Relives Being Slashed by Homeless Man: 'There Was Blood Everywhere'

School head Steve Cole told reporters that the blade had been blunted with duct tape and foam, calling the incident a “very unfortunate mistake.”

“It was an unfortunate, isolated incident which we are very disturbed about,” Cole told ONE News.

Critics took to the school’s Facebook page to express their incredulity that the school would use a real blade in a student production.

“One would think that instead(sic) of taking all that time to allegedly wrap a real razor over and over in tape, someone could have built a safe, realistic looking razor as a prop. Seriously?” one person wrote.

WorkSafe New Zealand, the government agency that investigates workplace health and safety, had launched a probe into the incident.

“I’m very confident the health and safety situation was strong,” Cole said, saying that he does not expect teachers who oversaw practice and the production to face disciplinary action.

Cole said the prop had been used throughout rehearsals of Stephen Sondheim’s 1979 London-based musical about “the demon barber of Fleet Street” since January.

Read: Waiter Gets 120 Stitches After Being Slashed While Working at Diner

While some parents were initially concerned about the subject matter, the show went on, ONE News reported.

“To some, the macabre, blood-soaked Sondheim classic, Sweeney Todd, may seem an odd choice for a school musical, however, once brought to the Saint Kentigern stage, there is no doubting that this is a theatre piece that raised the bar and challenged our student actors, musicians and stage crew on many levels,” the school posted on its Facebook page before the first show, which it called a “sophisticated musical.”

“The production shows that challenging material can be delivered, and delivered well, when you have the right cast and the right creative team,” the school wrote.

The school was slated to put on four showings, but canceled the second night’s show in light of the incident.

Watch: How to Defend Yourself Against a Slasher: Drag Attacker's Arm to Ground