Local media report the bus was full of students who were on their way to school on the western side of Savaii.
The students were rushed to Sataua District Hospital for emergency treatment.
Eyewitnesses say the wooden bus swerved to avoid another vehicle and it rolled over and split into pieces.
The bus was transporting students from Falelima, Tufu and Neiafu to the Asau Secondary School when the accident happened.
Authorities are investigating the accident.