Updated at 11:05 a.m. EST.
Security forces said they arrested dozens of people for violating an anti-looting curfew and rescuers found signs of life in a toppled building on Monday as Chilean officials struggled to bring aid to victims of a quake that.
"We are confronting an emergency without parallel in Chile's history," Bachelet declared Sunday, a day after the magnitude-8.8 quake - one of the biggest in centuries - killed at least 708 people and destroyed or badly damaged 500,000 homes.
Some coastal towns were almost obliterated, first shaken by the quake, then slammed by a tsunami that lifted whole houses and carried them inland and that reduced others to piles of sticks.
In Concepcion, the big city closest to the epicenter, police chief Eliecer Soler said officers arrested 55 people for violating a curfew imposed after looters sacked nearly market in town.
CBS News correspondent Mark Strassmann reports that with no electricity and scarce supplies, desperation mounted quickly and some survivors' minds turned to grabbing anything they could find in damaged shops.
The government deployed a reported 10,000 troops to try and maintain control in the hardest-hit regions south of the capital, where soldiers could be seen on the streets, reports Strassmann.
Across the highway from a looted supermarket, rescuers heard the knock of trapped victims inside a toppled 70-unit apartment building and began to drill holes through thick walls trying to reach them, said fire department Commander Juan Carlos Subercaseux.
Firefighters had already pulled 25 survivors from the building, as well as eight people who died.
Only the chop of military helicopters flying overhead broke the silence demanded by rescuers straining to hear signs of life within the building.
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At least a few looters re-emerged to rob a market on Monday despite Bachelet's order placing the city's security under military command.
On Sunday, ingenious looters used long tubes of bamboo and plastic to siphon gasoline from underground tanks at a closed gasoline station.
Eduardo Aundez, a Spanish professor, watched with disgust as a soldier patiently waited for looters to rummage through a downtown store, then lobbed two tear gas canisters into the rubble to get them out.
"I feel abandoned" by authorities, he said. "We believe the government didn't take the necessary measures in time, and now supplies of food and water are going to be much more complicated."
Looters even carted off pieces of a copper statue of South American independence fighter Bernardo O'Higgins next to a justice building.
Efforts to determine the full scope of destruction were undermined by an endless string of terrifying aftershocks that turned more buildings into rubble - and forced thousands to set up tents in parks and grassy highway medians.
"If you're inside your house, the furniture moves," said Monica Aviles, pulling a shawl around her shoulders to ward off the cold as she sat next to a fire across the street from her apartment building.
As if to punctuate her fear, an aftershock set off shuddering and groaning sounds for blocks around.
"That's why we're here," she said.
In another part of the city, eight Peruvian families shared a four-story building - the bravest living inside the cracked building, the others in tents out front.
"We've received help from the neighbors, from passing taxis and from other people who have offered us a coat or something to eat," said Samantha Fernandez, who offered space to boyfriend Jose Luis Jacinto after he fled his room during after the quake.
Bachelet ordered troops to help deliver food, water and blankets and clear rubble from roads, and she urged power companies to restore service first to hospitals, health clinics and shelters. Field hospitals were planned for hard-hit Concepcion, Talca and Curico.
Bachelet also ordered authorities to quickly identify the dead and return them to their families to ensure "the dignified burials that they deserve."
The U.N. said Monday that it wouldfollowing Bachelet's announcement she was seeking international aid.
U.N. humanitarian spokeswoman Elisabeth Byrs said Chile was seeking temporary bridges, field hospitals, satellite phones, electric generators, damage assessment teams, water purification systems, field kitchens and dialysis centres.
"We are prepared to provide assistance," Byrs told The Associated Press in Geneva. "It could be quite fast, given that our experts are on standby and were alerted in the region."
Secretary of State Hillary Rodham Clinton said Monday the United States is ready to work "in solidarity" with the leaders of Chile to provide disaster assistance to the earthquake-stricken country.
Speaking to reporters while traveling in Montevideo, Uruguay, Clinton said the Chileans had asked for communications equipment and said she will be bringing some with her when sheTuesday.
Clinton said more likely will come after that, saying that "one of the reasons they have asked me to continue my trip is to assess whatever else they might need and immediately begin the process of providing it."
Earlier, U.S. Ambassador Paul Simons said he knew of no American deaths from the earthquake, but stressed that officials were having a difficult time getting information from Conception, the area most devastated by the quake.
In an interview by telephone with CBS's "The Early Show," Simons said, "We do not have any confirmed reports of Americans who have died." He added that while officials have been able to contact "a few" of the estimated 1,000 Americans in Chile, "information is still very, very scarce."
Simons said that while life is returning to normal in the capital of Santiago, the Concepcion area near the epicenter of the magnitude 8.8 quake on Saturday suffers from "major devastation," where power is out and water is in short supply.
Simons' point illustrated what Strassmann dubbed "a tale of two quakes," referring to the minimal level of damage in the capital city compared to the utter devastation further south.
Defence Minister Francisco Vidal acknowledged the navy made a mistake by not immediately activating a tsunami warning after the quake hit before dawn Saturday. Port captains in several coastal towns did, saving what Vidal called hundreds of lives.
Thirty minutes passed between the quake and a wave that inundated coastal towns, leaving behind sticks, scraps of metal and masonry houses ripped in two. A beachside carnival in the village of Lloca was swamped in the tsunami. A carousel was twisted on its side and a Ferris wheel rose above the muddy wreckage.
Officials said at least eight people died and eight were missing on Robinson Crusoe Island, where it the tsunami drove the sea almost 2 miles into the town of San Juan Bautista.
In Washington, the State Department urged Americans to avoid tourist and other nonessential travel to Chile. U.S. citizens in Chile were asked to contact family and friends in the United States, whether by telephone, Internet or cell-phone text messaging.