(Updates with night shift cancelled at Andina)

By Antonio de la Jara

SANTIAGO, July 10 (Reuters) - Chile's Codelco suspended copper production for an entire day at one of its four mining divisions on Tuesday and curbed operations at another plant following violent protests by striking workers.

The disturbances were the most serious yet in a two-week stand-off between Codelco, the world's biggest copper miner, and subcontracted workers who are demanding improved pay and conditions.

Codelco, which provides the world with more than 10 percent of its copper, stopped extracting minerals at its El Teniente division in central Chile after protesters wrecked trucks carrying copper from the mine and hurled stones at buses transporting workers to their shifts.

Chilean television showed the trucks strewn across a road with their tires deflated and wind screens smashed. Piles of copper cathodes were still strapped to the trailers.

Extraction resumed in the afternoon and a Codelco spokesman told Reuters the situation had returned to "complete normality".

The division continued producing copper throughout the stoppage, but only because it was using existing mineral stock.

El Teniente, 65 miles (100 km) south of Santiago, is the second-largest of Codelco's four mining divisions and home to the world's biggest underground copper mine.

The division produced nearly 420,000 tonnes of copper last year, around 23 percent of Codelco's total output.

ANDINA OUTPUT SUSPENDED

Codelco, which produces some 1.8 million tonnes of refined copper a year, said output remained suspended at its Andina division, 50 miles (80 km) north of Santiago, after a transport worker was seriously injured in disturbances on Monday.

It said the worker suffered a fractured cheek and impaired hearing and vision after being hit by a rock thrown at the bus he was traveling in.

Codelco spokesman Antonio Varas said Andina's operations would remain suspended until Wednesday morning, and possibly for longer if the violence continues to jeopardize worker safety.

"The midnight shift isn't going up (to the mine) for safety reasons," he told Reuters. "The mine will remain paralyzed at least until Wednesday morning when we'll assess the situation."

Andina is the third-largest of Codelco's divisions and produced 248,000 tonnes of refined copper in 2006 -- some 14 percent of Codelco's total.

The violence comes 15 days after subcontracted workers at Codelco launched what they describe as a nationwide strike.

The workers are not employed directly by state-owned Codelco but perform tasks like earth clearing, catering, truck driving and cleaning at Codelco mines.

They say they want their salaries brought more into line with the company's unionized staff, who have enjoyed ample pay raises and bonuses as the copper price has soared in recent years, boosting Codelco profit.

Codelco says it cannot meet the main demands of the subcontracted workers because it is not their direct employer.

The company held talks with leaders of the strike on Tuesday and, in a statement issued by Codelco, both sides in the dispute condemned this week's violence.

Codelco said less than 10 percent of the 30,000 subcontracted workers at its facilities were involved in the protests.

COLLAHUASI STRIKE

The trouble at Codelco comes at the same time as a strike by workers at one of Chile's largest privately owned copper mines, Collahuasi, in the extreme north of Chile.

Workers at the plant extended their strike into a second day on Tuesday but a union source said the two sides were due to meet in the evening for the first time since the action started, offering hope of a resolution.

Collahuasi, majority-owned by industry heavyweights Xstrata Plc <XTA.L> and Anglo American <AAL.L>, produces around 8 percent of Chile's copper.

The Collahuasi strike prompted a spike in the price of copper in international markets on Monday but prices subsided on Tuesday.

(Additional reporting by Gideon Long and Manuel Farias in Santiago)

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