Adds state of emergency and curfew declaration in paragraphs 2, 6

By Fabian Cambero and Alexander Villegas

SANTIAGO, Feb 25 (Reuters) - A massive power outage across Chile plunged the country's capital Santiago into darkness on Tuesday and knocked out electricity to major copper mines in the country's north, buffeting global metal markets.

Hours after the outage began and as darkness fell, Chile's government announced a state of emergency and established a curfew from 10 p.m. to 6 a.m. (0100 to 0900 GMT) from the northern region of Arica to the southern region of Los Lagos.

The widespread blackout was caused by a transmission line failure in the country's north, Interior Minister Carolina Toha said, ruling out a cyber attack as a cause.

Chile's largest power cut in years saw streetlights in the capital go dark, while sirens from emergency vehicles blared across the city, according to Reuters witnesses. The Santiago metro, which transports millions of passengers, was closed and passengers were evacuated from stalled trains.

"There's nothing. There's no cash. No money. Nothing," said Jose Luis Orlandini, who was eating in downtown Santiago when the outage hit.

The interior ministry said it was deploying the armed forces across the country to help maintain order.

The head of Chile's National Electricity Coordinator $(CEN.AU)$, Ernesto Huber, said there was still no time frame to restore electricity across the country, but areas in the north and south had started to regain power.

"We've activated several power stations, mainly hydroelectric stations," Huber said, adding CEN was still investigating the cause of the outage.

Huber said companies were working to restore power "as soon as possible" and the agency would provide a more detailed update at 9:30 p.m.

The outage hit areas from the mining-intensive north to the central and southern regions home to most of the Andean country's population, and operations at key copper mines were affected. Chile is the world's top copper producer.

Escondida, the world's largest copper mine, was without electricity, a source close to the matter told Reuters, while state-owned copper miner Codelco said all its mines had been affected.

Chuquicamata, Andina, Salvador and El Teniente mines were without power and its other mines were using backup power generation to operate on a partial basis, Codelco said.

Antofagasta ANTO.L and Anglo American AAL.L both said that their mines were operating with generators.

The power outage affected the country from the northern Arica and Parinacota region to the southern Los Lagos region, according to Chile's national disaster prevention and response service SENAPRED. No emergency situations have been reported.

Chile's DGAC Civil Aviation Authority said that Santiago's Arturo Merino International Airport was operating normally but LATAM Airlines LTM.SN said some flights could be affected by the outage.

Toha said that power should start coming back online in the "coming hours."

"We hope that what we've been told will happen, that in the next few hours we'll have electrical service back," Toha said. "And if that's not the case, we'll have to take different measures."

(Reporting by Fabian Andres Cambero, Alexander Villegas and Rodrigo Gutierrez; Editing by Rosalba O'Brien and Sonali Paul)

((david.aliregarcia@thomsonreuters.com; +52 55 5282 7151; Reuters Messaging: david.aliregarcia.thomsonreuters.com@reuters.net))