The bus was travelling between Casablanca and the rural region of Ait Attab, near the town of Beni Mellal at the foot of the High Atlas mountains.
The injured were taken to a hospital in Khouribga and an investigation has been opened into the accident.
Road accidents, often deadly, are relatively frequent in Morocco and other North African countries.
An average of 3,500 deaths and 12,000 injuries have been recorded annually in Morocco, according to the National Road Safety Agency, with an average of 10 deaths per day.