The miners were working in a hole about 328 feet deep at the time, Radio Okapi reported.
The accident occurred Monday near Pangoy in Orientale province, about 75 miles from the city of Mambasa.
The region has extensive resources of tantalite and gold.
The administrator of the Mambasa Territory decried the deaths. He said many people had taken up the dangerous work after clashes between the Congolese army and militia leader Paul Sadala had forced them to flee their villages.