March 15 (Bloomberg) -- Chile's President Sebastian Pinera said the South American country will face power shortages for another seven days after an outage left 80 percent of the population in darkness for more than two hours yesterday.

"We are going to have an unstable electric system for the next seven days," Pinera told reporters in Santiago today. Power lines "that may have been damaged during the earthquake" will be checked and repaired in coming days, he said.

The power cut, the result of grid damage from last month's earthquake, affected a 2,000-kilometer (1,243-mile) stretch of the country and struck at about 8:43 p.m. local time yesterday. The outage extended from the Atacama Desert in the North to the Chilean lakes in the South, plunging locals into darkness and forcing mines to switch on emergency generators.

Service was reconnected in some areas of Santiago within an hour yesterday and was normal in all areas of the country today, with the exception of the Bio Bio region, the national emergency office said in a statement on its Web site. In Bio Bio, one of the areas hardest hit by the temblor last month, electricity was restored to 80 percent of the population by 11:00 a.m. today, the emergency office said.

"Things like this could happen in the future," Energy Minister Ricardo Raineri told reporters in Santiago yesterday. "Recovering the systems is a difficult task" after the Feb. 27 quake, and there may be blackouts for "months," he said.

Chile's main power grid, called the Sistema Interconectado Central, was affected following a disruption at Charrua, the system's biggest substation, 431 kilometers south of Santiago. The 8.8 magnitude earthquake that devastated central Chile last month has left the power grid "fragile," Raineri said.

Pinera said the government has committed to repairing a damaged transformer in the next 48 hours.

Aftershocks

A magnitude 6 aftershock hit offshore Maule, 360 kilometers southwest of Santiago, at 8:08 a.m. local time today, the U.S. Geological Survey reported on its Web site. There were no reports of damage or injuries, Chile's emergency office said.

Codelco, the world's largest copper producer, said the Andina, El Teniente and Salvador mines were operating normally after back-up systems were used to keep operations going during the outage, a company official briefed on the situation said in a telephone interview today.

Antofagasta Plc said in an e-mailed statement that the cut had "no material impact" on operations at its Los Pelambres copper mine after an emergency power system was turned on.

BHP Billiton Ltd., the world's largest mining company, said its Spence, Cerro Colorado and Escondida mines were unaffected because they are connected to a different power grid in the north of the country. Escondida is the world's biggest copper mine.

Xstrata Mines

Xstrata Plc mines in northern Chile are also unlikely to have been affected by electricity cuts, spokeswoman Viviana Alarcón said in a telephone interview from Santiago.

All of Anglo American Plc's copper mines in Chile have been back online since early today and production loss was "minimal," spokesman James Wyatt-Tilby said in an e-mail reply to questions.

Chilean President Sebastian Pinera told reporters in Santiago on March 12 that he plans to tap copper savings and may borrow abroad to pay for the estimated $30 billion cost to repair damage caused by the earthquake.

Pinera said he plans to rewrite the 2010 budget to free resources for a reconstruction fund. Chile has $11.3 billion invested overseas in an economic stabilization fund that the government can use to finance a budget deficit.