SANTIAGO/ANTOFAGASTA - A striking union at BHP's huge Escondida copper mine in Chile has rejected a company request to pause its action and come back to the negotiation table, with workers digging in as they seek a larger slice of profits in contract talks.

The union began a strike on Tuesday at Escondida, the world's largest copper mine, after contract negotiations collapsed, a move which could affect production at the mine and global prices if no quick resolution is found.

BHP and the union held a preliminary meeting on Wednesday to try to close the gap between the two sides and get back to formal talks, but the attempt failed, both sides said.

"The company suggested to the union the option to pause its strike until 8pm today, to resume talks," BHP said in a statement, indicating it was open to boosting its offer. "The union did not agree to the temporary suspension of the strike."

The union in its own statement accused the company of "anti-union" practices by replacing workers and said that BHP had imposed too many conditions on restarting talks.

"The demands and conditions of the company made it impossible to open talks," it said, citing a tight deadline from the company which didn't give enough time to consult its members.

The union added that the strike was keeping the Los Colorados concentration and electrowinning plants fully offline. BHP said the mine continued operating under a contingency plan.

"The strike is only effective for workers who are part of the collective bargaining payroll, not workers from other groups, unions, collaborating companies and minimum services approved by the authority," it said.

A few hundred workers began building an encampment at Puerto Coloso in the northern city of Antofagasta on Wednesday, BHP's exclusive port for shipments, which also houses its desalination plants, according to a Reuters witness.

A report by BTG Pactual, a Brazilian investment bank, said that BHP could lose between $25 million and $30 million a day if the strike goes on like the 2017 strike that lasted 44 days. It added that the strike hurt Chile's GDP.