Tuesday's emergency declaration suspends constitutional liberties of speech and assembly in the southeastern province for 30 days. The government also ordered the arrest of protest leader Herbert Huaman, the Los Angeles Times reported.
The violence broke out after President Ollanta Humala described demonstrators as leftist radicals, the newspaper said.
Protesters say mining firm Xstrata Copper doesn't hire enough local workers, violates environmental laws and doesn't give enough mining royalties to the local municipalities.
The Swiss-based mining company said it deeply regrets the violence and is asking municipal authorities in the province to "facilitate and promote a dialogue process that leads to resolving the social unrest that the capital of the province is currently living."
Xstrata said it is committed to "openness and dialogue" but said the social unrest "has been promoted by a group of leaders that incite violence, leading to the death of innocent people. We hope to see a responsible transition to democratic processes allowed within the rule of law."