According to news wire services AFP and Reuters, the blast at the La Preciosa mine in the Sardinata municipality in Norte de Santander may have been caused by a methane gas accumulation.

AFP quoted mayor Yamile Rangel as saying Wednesday afternoon local time that between 13 and 19 workers remained trapped; earlier in the day that number was 30.

Four miners were confirmed dead at the scene, she added, while a fifth died en route to a medical facility.

A senior Sardinata municipal official was quoted by the news outlets as saying that it was not yet clear exactly how many were trapped because the explosion occurred at 6.30am during a shift change.

Provincial governor William Villamizar told radio station RCN that the blast "exploded like a cannon shot, creating a flame inside the mine" and that rescuers and other emergency personnel were onsite.

“We understand that it is very difficult to survive an explosion of that nature," he said.

The accident is not the first for the mine; six workers died and two others were injured last October in a similar accident, and 30 others were killed in 2007.

Nine workers were killed at two small operations in the country’s Cundinamarca Province in November.

Almost 100 miners died in Colombia’s coal mines in 2010, according to federal statistics. The country is the world’s fifth-largest coal exporter.