The accident, which saw the bus come off a winding road to fall 24 metres (80 feet) into a ravine in the upland province of Nueva Ecija on Tuesday, also left 46 injured with four still in a critical condition, said Senior Superintendent Antonio Yarra.
"The wheel burst and that caused the bus to fall into ravine. It seems that it (the bus) was overloaded. Because of the overloading, it was beyond the capacity of the wheel to hold," Yarra, the provincial police chief told AFP.
He said a count determined there were 77 passengers on board, much higher than earlier estimates.
He declined to say who might be held responsible as the investigation was ongoing.
Road accidents are common in the Philippines, where old, badly maintained buses often drive on poorly lit roads.
In February, 13 students and a driver were killed while on holiday in a mountainous region when their bus slammed into a post.
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