The incident occurred yesterday in Kolwezi in the mineral- rich province of Katanga, where scores of impoverished illegal miners risk their lives in search of minerals including copper and cobalt.
"Fifteen artisanal miners died yesterday in a tunnel in Kolwezi," Mayor Deoda Kapenda told AFP.
"The miners died by suffocation in a tunnel more than 20 metres deep. It was not a landslide."
The victims also bore burn marks of unclear origin, he said.