The men are believed to have drowned after water from a burst dam flooded the shafts and underground tunnels they were working in.
Police said rescue teams were trying to pump out the water and search for bodies and any survivors.
According to reports, illegal miners in Battlefields, 175 km west of Harare, had entered shafts on land owned by RioZim and another firm in search of gold.
It added that the two mines, called Silver Moon Mine and Cricket Mine, are run by registered companies.

Kenya tourist helicopter crash kills seven
US, South Korea to cut length, scope of military drills after Trump order
Central African Republic gold mine collapse kills at least 100
Israeli airstrike kills nine Palestinians at Gaza police station
Thai schools hold shooting response drills after deadly school attack