The accident took place around 10 pm (0300 GMT) Friday on the highway between the capital Quito and Andean city of La Mana, police Colonel Cristian Barreiro said in a video released by the Ecu911 emergency service.
National Transit Agency chief Pablo Calle ordered the suspension of the vehicle's operator, saying the bus had not been properly inspected and "never should have been on Ecuadoran roads."
Survivors were rushed to hospitals in Quito and Santo Domingo province, while authorities said they were working to identify the fatalities.
Health Minister Veronica Espinosa said that of the 30 injured, 16 had been released and 14 were hospitalized, one of them in intensive care.
"My heartfelt condolences to the families of the victims," wrote President Lenin Moreno on Twitter. "In the midst of pain, may you find peace in your heart."
Road accidents are among the major causes of death in Ecuador.
Earlier this year 20 people were killed in a three-vehicle crash on a coastal road.
In a separate