The vehicle overturned a few kilometers from the city of Taza in the country's mountainous northeast.
In August, 23 people were killed and 36 injured when their bus overturned on a bend east of Morocco's economic capital Casablanca, one of the deadliest such accidents in recent years.
An average of 3,500 road deaths and 12,000 injuries are recorded annually in Morocco, according to the National Road Safety Agency, with an average of 10 deaths per day.
Long-distance buses are widely used in Morocco, especially in rural areas where many people lack the financial means to own a car.
Road accidents are common and often result in fatalities.
Authorities have opened an enquiry into the disaster.