The Excel No. 3 mine outside Pikeville had to be evacuated and shut down because of the fire. No one was injured.
The mine will be closed only temporarily until the fire can be extinguished. The mine is operated by MC Mining, a subsidiary of Alliance Resource Partners in Tulsa, Okla.
Employees discovered the fire late Saturday night.
Charles Wolfe, spokesman for the Kentucky Environmental and Public Protection Cabinet, said crews continued pumping nitrogen and water into the mine on Wednesday through holes drilled from the surface to try to suffocate the fire.
Conditions inside the mine are being monitored by fiber optic camera and by gas-detecting instruments.