The minibus was driving on a narrow dirt road in the northern Mountain Province on Tuesday when it swerved and fell into a 75-metre (250-foot) ravine, said provincial police chief Senior Superintendent Fortunato Albas.
The vehicle was packed with people who were returning from a victory party for a village candidate in last month's elections, he added.
Heavy rains had made the road slippery, possibly leading to the accident, Albas said.
Minibus safety: A code of practice
