The bus was carrying more than 30 people when its brakes malfunctioned and it toppled into a ditch in the northern province of Abra yesterday, police said.
One person died on the spot and four others in hospital, said regional military spokesman Superintendent Davy Vicente Limmong.
Twenty-eight others were injured in the crash, which came a day after a tourist bus plunged into a deep ravine in a remote northern mountain pass on Friday.
Fourteen people were killed in that accident, including a Canadian man and Dutch woman.
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Also among the dead was a popular Filipino comedian and his artist friends who were supposed to visit a tribal area.
Presidential spokesman Herminio Coloma said that in the wake of the accidents, a nationwide safety audit of all public transport had been ordered.
"We are investigating the roadworthiness of all types of public transportation, specially buses and public utility vehicles that are the main mode of transportation nationwide," Coloma said on public radio.
Old buses are the backbone of land transport in the Philippines. But they have been involved in frequent accidents due to poorly-lit and badly-maintained roads and drivers working long hours.