Five of the victims died at the mine's entrance and by afternoon two bodies had been removed from the mine with another 14 left to recover, said the provincial Colombian Red Cross director, Johel Enrique Rodriguez.
He told The Associated Press that rescuers had seen the rest of the bodies, which he said were covered in burns and scattered throughout the kilometer-long (0.6 mile-long) tunnel that extended horizontally beneath a verdant mountain.
Gabriel Tamayo, manager of the La Preciosa mine in Sardinata, 255 miles (410 kilometers) northeast of the capital, Bogota, would not speculate on the cause.
But Colombian Red Cross rescue chief Carlos Ivan Marquez said preliminary indications pointed to a methane gas buildup. A methane buildup was believed to have caused of an explosion at the mine in 2007 that killed 32 miners.
Such a blast "is like a kind of cannon shot and creates a flame within the mine and obviously has tragic consequences," William Villamizar, governor of the Norte de Santander province, where the mine is located, told RCN radio.
Officials said the explosion happened just before 7 a.m. during a shift change.
"I refuse to work here any longer," miner Luis Chacon told RCN television at the scene. He called La Preciosa "a killer mine."
The mine met legal safety requirements, said Edgar Fabian Morales, national safety coordinator for the Colombian Institute of Geology and Mining.
But the Ministry of Mining and Energy said it would be shut down, at least temporarily, and Mining Minister Carlos Rodado went to La Preciosa to meet with its managers and victims' families.
The mine was closed for five months after the fatal 2007 blast so a larger ventilation system could be installed for the expulsion of methane. Tamayo said the mine produced 3,300 tons (3,000 metric tons) of coal a month.
Fatal mining disasters are relatively common in Colombia, South America's top coal producer.
In June, 73 miners were killed in a blast at a coal mine in Amaga, a town in the northwestern province of Antioquia. In November, nine miners died in two different accidents in Cundinamarca state in central Colombia.
Relatives of miners who lost their lives in Wednesday's blast said there weren't any other employment opportunities in the region.
"Here the only work that can be had is in the mines," said Analuz Acosta, whose 31-year-old son-in-law Jorge Eliecer Lara perished inside La Preciosa.
Lara left a wife and four children ages one to 6, she said.
He had survived the 2007 accident, said Acosta, but her 21-year-old son Alberto did not.
