At least 16 high school students celebrating their graduation and a driver were killed Sunday when the bus they were traveling in plunged into a ravine in northwest Colombia.

The group of students -- aged 16 to 18 -- from a school in Bello, near Medellin, were traveling from a Caribbean beach on Colombia's coast.

Twenty more were injured in the 40-meter plummet, and a source in the Bello mayor's office told AFP that officials were still working to determine how many of the victims were minors.

Antioquia Department Governor Andres Julian Rendon told media the cause of the accident remained under investigation.

In a video Rendon posted to social media, one of the survivors said "I was asleep and all of a sudden I heard screams, and from that moment on I don't remember anything."

The students had paid their way to the idyllic Caribbean beach towns Tolu and Covenas to celebrate graduation. 

Rescuers had to transport survivors out of the treacherous ravine on stretchers.

President Gustavo Petro offered condolences to affected families in a post on X.

"I don't like it when young people die. Even less when they're going to study or to relax happily," he wrote.

A police source told AFP the National Liberation Army (ELN) guerilla group operates in the area of the crash, which meant firefighters and officers had to take special security measures to carry out the rescues.

ELN rebels ordered civilians to avoid commercial travel for 72 hours in regions under their control starting Sunday, while they conduct military exercises.

On average, 22 traffic-related deaths a day were recorded in Colombia in 2024, road authorities reported.