Kaipara College students may have to attend other schools next week, while the extent of the school's asbestos problem is checked out.
Asbestos dust was found in the hall hall and administration block on Thursday night, after a routine check on water-tightness.
The school is closed until at least Wednesday, pending the results of air tests being done this weekend.
Principal John Grant said the school will reopen if it is safe but if not, students will have to go to nearby schools.
It was an important time for students preparing for NCEA exams, which started soon, he said.
"There is a lot of informal access by our students to our staff right across the NCEA period, and as well as a venue for the exams, enabling our students to get access to staff is also a concern."
The school was closed as a precaution yesterday and further tests are being done this weekend.
Ministry of Education head of infrastructure service Kim Shannon said once the results were back on Tuesday, the school would decide if it was safe to reopen.
WorkSafe and the Auckland Regional Public Health Service have been notified.
Ministry and school staff met on Saturday afternoon.
Asbestos dust was found in the school hall and in the administration block on Thursday night, during routine checks.
The discovery prompted a precautionary closure of the school yesterday while further samples were collected and air-monitoring tests carried out.
Principal John Grant said the dust appeared to have come from the roof of the school hall, which
was made of fibrolite, common in some buildings constructed in the 1960s and 70s.
The dust samples collected contained white and possibly brown asbestos, he said.
The Ministry of Education yesterday said it would work with WorkSafe on how to safely remove the asbestos.
The school should know by Monday what the situation is, and would be updating parents as quickly as possible via the college's website, Mr Grant said.