The incident happened when two galleries caved in at a mine in the Kolwezi area operated by Kamoto Copper Company (KCC), a subsidiary of Glencore.
“Tragically there were 19 fatalities today, with possible further unconfirmed fatalities,” Glencore said in a statement, which said there had been recurrent problems with illicit mining on its concessions.
Other reports suggest the death toll could be higher.
The Congolese site Actualite.CD reported at least 36 deaths.
“The illegal artisanal miners were working two galleries in benches overlooking the extraction area. Two of these galleries caved in,” the company said.
Glencore said KCC had observed a “growing presence” of illegal miners, with on average 2,000 people a day intruding on its operating sites.
“KCC urges all illegal miners to cease from putting their lives at risk by trespassing on a major industrial site,” Glencore said.
Illegal mining is common and frequently deadly in Democratic Republic of Congo, where safety is often poor and risk-taking high.
Figures indicating the scale of the problem are sketchy, given that many mines are illegal and remote.