(New throughout, adds details, background, comments, copper price)
By Fabian Cambero
SANTIAGO, Sept 22 (Reuters) - Workers at Escondida, the world's biggest copper mine, went on strike for 24 hours on Monday, calling the stoppage a "warning" as they seek improved working conditions.
The mine's powerful union had said last week it would call out its workers for 24 hours on Monday and again on Wednesday after it failed to reach agreement with management over issues related to working hours, health and safety.
The strike followed "a null result from talks with the company," the union head, Patricio Tapia, told Reuters on Monday.
Escondida is controlled by global miner BHP Billiton , while Rio Tinto also owns a 30 percent stake.
BHP did not immediately comment on the strike.
Workers did not board buses for the first shift on Monday, Tapia said.
Escondida, located at high-altitude in Chile's arid north, produced 1.19 million tonnes of copper last year.
That was equal to about 20 percent of the output from Chile, the world's top copper producer.
Last year, the union carried out a similar short stoppage over pay and conditions, which did not have a significant impact on production. The last time it carried out a major strike was in 2011, when workers downed tools for two weeks, hitting output hard and stunning the copper market.
On Monday metals traders were focusing more on worries over growth in top buyer China, leading London copper to fall to a three-month low.
No other mines have joined the strike, but the Chilean Mining Federation, which groups unions from privately-run mines like Escondida and Collahausi, issued a statement in support of the union's move and said it was "on alert". (Additional reporting by Silvia Antonioli in London, Writing by Rosalba O'Brien)