The accident took place around 7:20 a.m., local time, in Sitio Pagang, Barangay Tabulin, Bontoc Mountain Province, ABS-CBN reported.
Some witnesses told police the bus had engine problems but investigators said they were considering human error.
Among the dead were two tourists from the Netherlands and Canada, ABS-CBN reported.
Twenty-one people were taken to Bontoc General Hospital, three were admitted to Luis Hora Hospital and four were missing, the report said.
Rosie O'Donnell unveils nearly 50-pound weight loss
Justin Bieber crashes Drake Bell's album release party