Police are investigating the incident, after they were called to Haeata Community Campus in the suburb of Aranui just before 2pm.
Principal Peggy Burrows said the attack happened in the primary section of the school, and involved a student under the age of 16.
She said one teacher was cut on the palm of their hand and another received head injuries.
Burrows said the assault was witnessed by a number of staff and students.
The teachers were treated for their injuries, and were on leave for the rest of the week.
Burrows said the pair were now home with their whānau and did not require hospitalisation.
"Please check with your ākonga/student if you observe any evidence of distress or anxiety and contact the kura/school if they are having difficulty processing what they may have witnessed during this assault."
Burrows said there was plenty of support at Haeata for students who felt upset about what they witnessed.
Haeata Community Campus was also investigating the attack.
School was still planned to go ahead as usual on Thursday.
