At least 31 people died in southern Bolivia Monday when their bus plunged into a ravine after colliding with a pick-up truck, bringing to nearly 70 the number killed on area roads in recent days, investigators said.

The crash in southern Potosi department came two days after at least 37 people died when a bus heading to the Oruro Carnival, one of the biggest festivals in Latin America, collided with another bus near the city of Uyuni.

Monday's accident took place around 90 kilometers (60 miles) north of the city of Potosi and also involved Oruro festivalgoers — this time people leaving the Andean city after the weekend carnival, which attracts tens of thousands of revelers.

Investigators said they suspected the pick-up driver of causing the collision by crossing lanes into oncoming traffic, ramming headlong with the bus, which plummeted down a gorge half a kilometer deep.

Twenty-two people were injured.

The pick-up driver was taken into custody in hospital, where he was being treated for his injuries, police spokesman Limberth Choque told AFP.

The public prosecutor's office said the driver was being investigated for possible homicide and causing serious injury.

Forensic experts were combing the accident scene for evidence.

The driver of one of the buses involved in the weekend crash had allegedly been drinking and was speeding when he too swerved into oncoming traffic, prosecutors said.

Six foreigners were among those killed: five Peruvians and a three-year-old German girl.

Horrific smashes are all too frequent on Bolivia's narrow, mountain roads.

Road accidents kill an average of 1,400 people every year in the country of about 12 million inhabitants, according to government data.

Potosi accounts for 10.6 percent of all the traffic accidents, according to the Bolivian Observatory of Citizen Security.

Over 120 people have been killed so far on the department's roads so far this year.

On 17 February, at least 30 people died after a bus plunged into a deep abyss on the outskirts of Potosi.

Authorities said speeding was the suspected cause of that crash.

In January, 19 people were killed when a bus careened off a road, also near Potosi.