A bus carrying Argentine border patrol officers crashed into a ravine in the northern province of Salta, killing 42 people.
A local emergency official said nine police officers were taken to hospital.
The vehicle was part of a three-bus convoy carrying officers of Argentina's gendarmerie, which patrols the country's borders.
Salta borders Bolivia, Chile and Paraguay.
Passengers on the other two buses were the first people onsite to attempt to save the officers trapped in the wreckage, officials said.
Border security has become a hot issue in Argentina as the country has emerged as part of a route used for smuggling Andean cocaine to Europe and for human traffickers sending Syrian refugees to the Western Hemisphere.
President Mauricio Macri, elected last month on a platform that included improving Argentina's rural roads, sent his condolences to families of the victims of the crash.
"We need to improve our highways so these things don't keep happening," he told reporters on the sidelines of a news conference in Buenos Aires province.
"The Argentine people must stand with these families," he said.
The local mayor, Gustavo Solis of Rosario de la Frontera, said the road where the accident occurred is known to be in poor condition.
"Those of us who know the area try to avoid driving at night," he said.