The explosion occurred in the same mine where another blast killed 32 workers in 2007.
Sardinata Mayor Yamile Rangel Calderon told The Associated Press that at least five workers were killed and five others injured. Speaking by telephone from the site of the accident, she said the injured men reported that 16 others were still trapped.
Rescue workers had been unable to enter the mine due to a collapse, she said.
The Colombian Red Cross earlier had reported 32 were trapped at the La Preciosa mine in Sardinata, some 250 miles (400 kilometers) northeast of the capital of Bogota.
"The initial report from my people there says that the cause was methane gas," Red Cross rescue chief Carlos Ivan Marquez told The Associated Press.
Norte de Santander provincial Gov. William Villamizar told RCN radio that the explosion occurred about 6:30 a.m. (1130 GMT) during a change of shift for the workers.
An explosion of that kind "is like a kind of cannon shot and creates a flame within the mine and obviously has tragic consequences," he said. The governor estimated that 32 people were trapped and said that it is usually difficult to find survivors after such accidents.
The mine is legal, according to Edgar Fabian Morales, national safety coordinator for the Colombian Institute of Geology and Mining, but he said he had no details on the incident.
"It was one of the best mines. It is big. It complies with the requirements of the law," the mayor said.
An explosion at the mine in February 2007 killed 32 workers. Authorities said it was probably caused by a buildup of methane gas ignited by a spark.