The rest of the estimated 45 passengers were plucked by rescuers who struggled with ropes to descend down the ravine to reach the bus wreckage in Nueva Ecija province's Carranglan town, said disaster-response officer Mark Raymond Cano.

Many of the passengers had serious injuries and were taken to a hospital, he said.

Carranglan police chief Robert de Guzman said the bus from northern Isabela province was on its way to Ilocos Sur, a tobacco- and rice-growing region also in the country's mountainous north, when it crashed shortly before noon.

Poorly maintained passenger buses, inadequate road safety features and weak enforcement of local transport laws have been blamed for many vehicular accidents.

In February, a sightseeing bus carrying college students on a camping trip lost its brakes on a steep downhill road and smashed into a concrete electrical post in Tanay town in Rizal province east of Manila, leaving 15 people dead.