At least 39 migrants were killed and about 20 were injured early Wednesday when the bus they were riding in western Panama tumbled off a cliff, authorities said.

Officials did not immediately report nationalities, but the migrants had crossed the treacherous Darien Gap from Colombia.

The Panamanian government typically moves migrants who have crossed the Darien to a camp near the Costa Rica border on the other side of Panama. The migrants pay for the bus tickets, but the buses are only for migrants. There are usually two drivers, as well as personnel from the National Immigration Service.

Samira Gozaine, director of Panama’s National Immigration Service, said it appeared the bus driver had passed the entrance to a shelter in Gualaca and when he tried to turn around to get back on the highway, the bus collided with another bus and went off the cliff.

Images from the scene showed a broken guardrail on a curve in a forested area just a couple hundred yards beyond the shelter. The bus was carrying 66 migrants to the Los Planes shelter.

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Ambulances carried the injured to the nearest hospital in David.

“This news is regrettable for Panama and for the region,” President Laurentino Cortizo said via Twitter.

It was the worst accident involving migrants in Panama in at least a decade. The flow of migrants through Panama surged in recent years as more risked the dangerous crossing as they tried to make their way north to the United States.

Last year, nearly 250,000 migrants crossed the Darien jungle – the majority Venezuelans – a record number that nearly doubled the total from the previous year. In January, more than 24,000 migrants crossed Darien, mostly Haitians and Ecuadoreans, according to Panamanian authorities.