The blast tore through a gas station in the town of San Martin, about 200 kilometres southeast of Bogota, late on Sunday night.
Local police said the Revolutionary Armed Forces of Colombia (FARC) were likely behind the attack.
“There are some 20 wounded and serious material damage,” police commander Colonel Jose Arnulfo Oliveros told AFP. “The entire area has been cordoned off and the victims are being cared for.”
Oliveros said the government will pay a 20-million-peso ($7,000) reward for information leading to the capture of the culprits.
The driver was reportedly heading for the petrol station. He jumped from the van before reaching the planned target and just before the explosion, a police spokesman told AFP.
"We are searching for this person, some of whose belongings were found in the area," he said.
In a separate incident on Saturday, a civilian was killed and a police officer wounded when a car loaded with explosives was detonated between Bogota and Caqueza.
On Friday, five people, including two children, were burned to death by a car bomb, apparently meant for a passing military patrol in the oil-rich northeastern state of Arauca.
Arauca is one of Colombia's most troubled provinces and has been the scene of many battles between FARC and government soldiers. The National Liberation Army, a smaller yet equally violent rebel group, also operate in the area.
US special forces troops have been there since January, training Colombian anti-guerrilla units to defend an oil pipeline from bomb attacks.