According to CNN and the Associated Press, the group was trapped sometime Wednesday afternoon at the El Desespero operation in Angelopolis about 150 miles (245km) from Bogota.
The National Police commander told CNN that some of the miners’ belongings had been located but it appeared the miners were dead.
Colombia’s Ingeominas oversight agency told the global news service that the mine had flooded but no speculation on the cause was disclosed.
However, AP sources said crews had hit a source of water while working which flooded and collapsed the operation.
Marisela Bustamante told CNN affiliate Caracol TV her two brothers were beginning their first day on the job.
“My two brothers went inside the mine at 2pm and about 10 minutes later, the tragedy occurred,” she told the outlet.
The only known survivor is worker Norberto Isaias, who reportedly escaped the mine.
In a statement, Ingeominas told various media outlets that the mine was illegal.
Owner Arnulfo Velasquez, however, told CNN that his operation had all necessary insurance and was legally producing.
According to industry data, between 2005 and 2010 almost 500 miners lost their lives in accidents.
Colombia is the fourth-largest coal exporter worldwide.
It is also the largest coal producer in the Latin American region, with major players such as Glencore, Drummond and Cerrejon operating in the country.