The health authorities in Ghana have detected 55 cases of coronavirus among students and staff at Accra Girls Senior High School in the capital.
Some 314 were tested in total. All the confirmed cases have been transferred to treatment and isolation centres, according to a joint statement by Ghana Health Service and the Ghana Education Service.
Ghana allowed final-year students back into classrooms last month to allow them to sit exams.
The first cases in schools were detected last Monday.
President Nana Akufo-Addo last week went into quarantine for 14 days as a precaution when a member of his close circle tested positive for coronavirus.