St John ambulance staff were quickly on the scene to administer treatment. Mr Grace said the two injured students were traumatised but should be okay.
The rest of the class were also shaken up: "I think they all got a big fright. A loud bang like that does tend to put you on edge."
An AUT spokeswoman said the explosion was an isolated incident, which was being investigated by the university.
"It's back to business as usual," she said. "The class has resumed, they're back into it."
There were five students in the class at the time, with one tutor. The remaining three students chose to remain in class and complete their lessons.