CALGARY -- A Calgary school is pivoting to online learning after a COVID-19 outbreak was declared -- and according to an internal note, hundreds of students are isolating at home.

Bowness High School in the city's northwest is officially listed as having five to nine cases either acquired or transmitted in the school.

It's prompted the principal to notify all students and teachers that they'll be behind a keyboard starting on Monday until March 16.

A letter sent to parents cites "operational capacity challenges" because of "the number of cases in a short time frame."

But while the case number may appear low, there are fears it'll grow drastically in the days ahead.

There have been rumblings in the community of birthday party attended by up to 30 Grade 11 students that prompted the spread.

CTV News has obtained a letter that says more than 600 students and 24 staff members are being required to isolate. That's more than half of the entire school's student body.

While that number -- and the party itself -- is still unconfirmed by health officials, another letter posted by the school Thursday says the outbreak was, in part, driven by students in Grade 11.

It says at least four cases were identified in the grade over the course of a few days.

"Three quarters of the Grade 11 student body and many associated staff members have also been identified as close contacts of these cases and will be required to isolate at home for up to 14 days," the letter reads.

Originally, the move to online class was only going to be for that grade, but a school-wide alert was called on March 3 after two or more cases were discovered.

Two days later, the count was up to at least five.

The school says during the coming week, all students "will be supported in maintaining course work during the designated period through Brightspace, Virtual Classroom and/or Google Meet."

The Calgary Board of Education did not agree to be interviewed for this story, but a statement reads, in part, "we all share the responsibility to follow all health and safety guidelines, whether in school or outside of school time, to reduce the impact of COVID-19 on schools and learning."

If any students or teachers are experiencing symptoms, they're urged to reach out to Alberta Health Services.

Sixty three schools in the province currently have at least five COVID-19 cases.

Of those schools, 20 have more than 10 cases.