About 100 hooded protesters have illegally entered Anglo American's Los Bronces copper mine in central Chile, seizing installations and setting up flaming barricades.
The global miner blamed a group of contractors and "unidentified people" for the violent occupation of parts of the mine and the takeover of outbuildings and trucks.
"This situation creates a serious risk to the safety and physical integrity of more than 1,500 people who are currently in Los Bronces and presents environmental risks in case the normal operation of our processes and operational controls is not restored," Anglo American Chile said in a statement (in Spanish).
The move comes as the union representing contractors at Los Bronces, one of Chile's largest copper operations, negotiate with their employers, who provide services to the mine. Anglo said it was a "facilitator" in the negotiations and appealed for both sides to continue their dialogue and call off the violence.
Los Bronces is Anglo's biggest operation in Chile, poised to become the world's No. 5 copper mine at its peak.It also said it had requested police intervention and announced that it would take legal actions to protect the rights and safety of its workers and the property.
In September, over 1,700 Los Bronces workers staged a one-week strike over wages.
Anglo American noted it was evaluating the impact of today's events on production as copper is the firm's second-largest contributor to profit after iron ore.
Its Chilean division alone - dubbed Anglo American Sur - is expected to produce between 600,000 and 630,000 tonnes of the red metal this year, and Los Bronces is the unit's biggest mine.
Last year, it produced 437,800 tonnes of the red metal, out of top copper exporter Chile's total 5.76 million tonnes.
Anglo owns 50.1% of the operation. Chilean state miner Codelco and Japanese trading houses Mitsui & Co. and Mitsubishi Corp. also have stakes in it.
Los Bronces, perched 3,500 meters high up in the Andes 65km north-east of capital Santiago, is also one of the few Anglo still has in Chile. Last year, the London-listed miner completed the $300 million sale of its 100%-owned Mantos Blancos and Mantoverde copper mines in northern Chile and announced intentions to also sell El Soldado mine and the Chagres smelter.