More than 500 students from Greenhithe School in Auckland have been sent home following a sewage spill.
The spill occurred this morning while unblocking work was being undertaken.
The school, with a roll of 540, made the decision to send the children home after consultations with the board of trustees chairman who contacted the Ministry of Education for official advice.
Acting principal Heather Walker said a small amount of excrement had spilled onto the surface of a grassed area which was "immediately fenced off yesterday afternoon by the caretaker''.
Ms Walker said they decided to send the students home because "we have children as young as five who are quite curious''.
"We were more likely to be criticised for not closing it,'' she said.
Ms Walker said contractors have been digging up the ground in search of the blockage.
Following the contamination of the grass area "gallons of disinfected had been sprayed,'' she said.
Students whose parents cannot be contacted will spend the rest of the day at school "safely ensconced in their classrooms''.
Ms Walker said alternative toilet facilities were available.