Rosas did not give the identities or causes of death of the victims.
Police and military crews exploring the underground site wore breathing equipment to guard against the possible noxious gases in the mine.
The state of Guerrero, where Taxco is located, is plagued by drug violence among rival gangs, and marked by brazen attacks on police and soldiers engaged in a crackdown on traffickers.
In an unrelated case, authorities arrested two brothers on Sunday named on Mexico's "Most Wanted" list for their ties to organised crime.
Rosas said the brothers, who are suspected members of La Linea drug gang, are linked with drug dealing, kidnapping, extortion, car theft and several murders in the north Mexico state of Chihuahua.