A report by the Tan Loi middle school in Buon Ma Thuot City said on Tuesday morning the girl was in a physical education class that involved running.
At around 7:30 a.m., after running for around 250 m, she was walking toward the finish line when she collapsed.
The teacher performed first-aid and called the school nurse. The girl was then taken to the Thien Hanh General Hospital where she later died.
Nguyen Thi Hong Thao, vice headmistress of the school, said the student had been in normal health and attending school regularly.
But doctors said later she had a cardiovascular disease, she added.
The Ministry of Education and Training permits students with chronic diseases, disabilities and illnesses to skip physical education classes at school.