A government statement says the number of injured has also risen, to 46.
Some of the injuries are grave, and the number of dead could increase further.
The bus ran off a foggy, rainy mountain road Friday and rolled about 650 feet (200 meters) downhill before a tree stopped its fall.
Disaster agency official Paul Sanchez said Saturday that the vehicle had a capacity of 45, but 84 were on board, including the driver. There was also cargo such as a refrigerator.
Authorities closed down the bus company's operations pending an investigation.
The driver was among the dead.