The accident occurred Friday night as the red-and-yellow cargo truck made its way back from a party in the provincial capital of Santa Teresa, an area about 310 miles (500 kilometers) southeast of Lima. It went off the road and fell about 650 feet (200 meters) into a deep ravine, ending up in the Chaupimayo river which courses through the ravine.
Rescuers equipped with little more than flashlights spent the night searching without success for survivors amid the twisted steel and large boulders, pulling bodies from the water. Authorities said bodies were found as far as 330 feet (100 meters) away from the impact site, suggesting they were thrown from the vehicle.
"We haven't found a single survivor," said firefighter Capt. David Taboada, who was leading the rescue operation.
Firefighters had said that 52 people died in the accident, but later in the day Santa Rita police issued a press release saying that the official death toll was 51, including 14 children.
The cause of the accident hasn't been determined, Taboada said, adding that the vehicle was "coming from a party in Santa Teresa at which a lot of alcohol was consumed."
Firefighters were placing the recovered bodies on a soccer field above where the crash took place.
Throughout the morning and day, relatives of the victims arrived to identify their loved ones.
Fedia Castro, mayor of the district where Santa Teresa is located, told Canal N television that rural farmers must rely on informal forms of transport, such as this cargo truck, because no public buses exist in the area.
The high-altitude roads of the Peruvian Andes are notorious for bus plunges, with poor farmers comprising many of the victims. Last year, more than 4,000 people were killed in such accidents.