The driver, who was among the dead, reportedly lost control of the wheel and veered off the road in the town of San Mateo, in central Boyaca department.
Authorities said the cause appeared to be a mechanical failure, but the vehicle, which was carrying 19 passengers, will be subject to revision, said Julian Alvarez, chief of Boyaca's Transit Police.
The head of the police department in Boyaca, Carlos Fernando Triana, said the 1967 model did not have the necessary paperwork showing it had undergone periodic mechanical tuneups.
"We are investigating all the details of this dramatic accident," said Triana, adding three died on the site and four others lost their lives after receiving medical attention.
"It appears the privately owned vehicle had been illegally providing public passenger service for some time," Triana said.
The injured, mostly farmers who were heading to a market, are treated at the San Mateo Hospital.
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