The young people were on a school trip to the city of Medellín when the accident occurred, said Governor Andrés Julián Rendon of the department of Antioquia in northwestern Colombia.
"The entire healthcare system has been activated to help in this emergency," he writes on X.
According to the news site Infobae, 16 of the 45 people on board have died. The young people, who are of high school age, were coming from the town of Bello when the bus plunged 80 meters into a ravine for unknown reasons.
Images from local media show the wreckage of the bus in the ravine while rescue workers carry people on stretchers.
Traffic accidents are common in Colombia. Last year, an average of 22 people died in traffic accidents per day, according to the country's traffic safety agency.
