Workers at the world's largest copper mine, in northern Chile, have begun an unexpected strike to demand improved working conditions and a bonus.

The work stoppage at Escondida mine, which employs an estimated 2,500 workers, began on Wednesday and was initially planned to last 24 hours.

"We're going to wait until tomorrow to see if the company gives us any signals. Once we meet we'll decide whether to extend the protest or take another type of action," Marcelo Tapia, a union representative, said.

The strike began after management refused to pay an annual bonus that is not covered in workers' contracts, which last year totalled approximately $5,000 per worker.

Tapia said workers are also asking for a system to keep track of overtime and the removal of surveillance cameras from inside mining lorries.

According to a union representative, all operations had been halted at the mine which is majority owned by BHP Billiton of Australia.

Management had no immediate comment on the strike.

The mine's union upset the copper market in 2011 by staging a two-week work stoppage, drastically reducing the mine's output.

Labour action has become common in Chile as workers seek to get their issues heard before the November presidential election.

Chile is the largest copper producer in the world, providing nearly one-third of global supply.

Source: Agencies