At least 41 Argentine police members were killed Monday after a bus they were traveling in flipped and fell off a bridge in the northern part of the South American nation.

Authorities say the crash happened early Monday while a convoy of three buses with gendarmes officers was traveling near Salta, a city about 932 miles north of Buenos Aires.

‘Between 50 and 60 border patrol officers were on board. Some are still trapped,’ provincial emergency director Ernesto Flores told the La Red radio station, reports Fox News.

Angel Marinaro, civil defense director for the province, told local station TN that for unknown reasons the driver of one of the buses lost control as the convoy was crossing a bridge.

The vehicle flipped and fell off the bridge, landing about 65 feet below. Local television images show an overturned bus and rescue crews working the scene.

Gustavo Solis, the mayor of Rosario de la Frontera – a city in the area – told the media that the road where the accident happened is known to be in poor condition.

Authorities say survivors are being taken to a nearby hospital.

Police said in a statement that visibility was good at the time of the accident and they are considering mechanical failure as a possible cause, according to Sky News.