At least 29 people died as a bus plunged into a ravine in the northern Philippines, in one of the country's deadliest accidents in years, officials have said.

Key points: Brakes believed to have malfunctioned as bus sped downhill

Brakes believed to have malfunctioned as bus sped downhill Sixth accident in the area in recent years

Sixth accident in the area in recent years Unsafe buses, lack of road safety and slack law enforcement blamed for accident rates

Bus passengers were screaming in horror as the driver repeatedly stepped on the apparently malfunctioning brakes before plunging into the deep ravine in Nueva Ecija province's Carranglan town, a survivor said.

The rest of the more than 50 passengers were retrieved by rescuers who struggled with ropes to descend down the 24-metre deep ravine to reach the wreckage, disaster-response officer Mark Raymond Cano said.

Many of the passengers were hospitalised with serious injuries and parents were separated from their children in the confusion.

"One child here sat beside her mother. The mother was dead," said Dr Napoleon Obana of the Veterans Regional Hospital, where some of the victims were taken.

TV footage showed a line of rescuers and villagers, some holding on to a rope to climb up on a grassy slope with a victim on a stretcher.

A throng of villagers waited in a clearing above them to help pull the victim to safety.

Dozens of passengers died when the bus they were travelling in apparently lost its brakes and plunged into a deep ravine, in one of the country's deadliest road accidents in years. ( Philippines Red Cross via AP )

Dr Cano said a preliminary investigation showed that the bus "lost its brakes and plunged down the ravine".

Passenger Ralph Raymond Grajo said he saw the driver repeatedly stepping on the malfunctioning brakes as the wayward bus was speeding along a downhill road.

The driver attempted to steer the bus to the right, but roadside houses made him veer back in the direction of the ravine as horrified passengers watched, Mr Grajo told local media.

"All the passengers were screaming and somebody in front me told everybody 'don't panic,' but many were already gripped by panic," he said.

Mr Grajo apparently fell off the bus as it rolled down the ravine and regained consciousness away from the wreckage with injuries to his feet and arms.

He said he was among the first to be rescued and brought to a hospital.

It was not immediately clear if the driver survived.

Tuesday's accident was the sixth in the area in recent years, a local village official said.

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

In February, a sightseeing bus carrying college students on a camping trip lost its brakes as it sped down a steep downhill road before smashing into a concrete electrical post in Tanay town in Rizal province east of Manila, killing 15 people.

AP