Three Dunedin schools have closed early due to a "significant" burst water main which has also shut Moana Pool.

Otago Boys' High School (OBHS) announced on social media it was closing at 11am - affecting exams scheduled in the afternoon.

It had not had water since 8am.

Trinity Catholic College and Arthur Street School were also closed for the day.

In an update on social media Dunedin City Council said a work around meant water supply was back on and Moana Pool would re-open by 2pm.

Contractors were still working to fix the original problem, which it called a "significant water burst" on Stuart St.

OBHS said it did not take the step to close lightly.

"We are aware of the disruption to students and families, however we feel that the care of the students and staff is most important at this time.

"We have also been in contact with the Ministry of Education regarding this situation.

"Without a water supply, toilet facilities and the canteen cannot operate, making it unsafe for staff and students to remain on campus."

Morning exams would continue unaffected until 12pm, but afternoon ones had been cancelled and students asked to check emails for rescheduling updates.

A Dunedin City Council spokesman said there had been a pipe failure on Stuart St.