A woman climbs over the debris of her destroyed house Monday in Dichato, Chile. Looting spread in earthquake-leveled parts of Chile on Monday even as army troops were deployed in armored vehicles and on horseback to restore order and protect shipments of food and water.

Santiago, Chile ? Security forces struggled to contain looting and clashes in this country’s second-largest city Monday, as tens of thousands of Chileans who lost their homes in Saturday’s earthquake camped out in the streets and waited for relief.

More than 10,000 troops have been deployed to patrol the city of Concepcion and outlying areas devastated by the 8.8-magnitude earthquake. But even as the first contingents fanned out on foot and in army tanks, they seemed largely unable to contain the chaos. In Concepcion, looters set fire to a department store and supermarket, sending a cloud of black smoke billowing over the city.

Francisco Vidal, the Chilean defense minister, announced that the government would impose curfews through today to control looting, and the mayor of Concepcion, Jacqueline van Rysselberghe, made a desperate plea for more troops and aid from the national government.

“Fear is everywhere; armed men with pistols are attacking residential homes,” van Rysselberghe told reporters, adding that even firefighters trying to distribute water had been attacked. “Send the largest number of troops possible.”

After initially declining to request foreign aid, President Michelle Bachelet on Monday officially sought assistance from the United Nations. Chilean officials called on the international community to donate temporary bridges, satellite phone equipment, water-purification systems, dialysis machines and electric generators.

The Chilean foreign minister, Mariano Fernandez, met with ambassadors to Chile on Monday to coordinate the aid. Secretary of State Hillary Rodham Clinton will discuss aid efforts with Bachelet when she arrives in Santiago today.

Clinton, who began a weeklong South American tour on Sunday, told reporters traveling with her that she was bringing 20 satellite phones and a technician on her plane in response to the Chileans’ request for communications equipment. She said she was continuing with a previously planned stop in Chile — only at the airport — in order “to assess whatever else they might need and immediately to begin the process of providing it.”

In Washington, State Department spokesman P.J. Crowley said Chile has also requested a field hospital and water-purification systems.

More than 700 people have been confirmed killed so far in the quake. The State Department estimated that about 18,000 U.S. citizens are in Chile, with about 1,000 in the hardest-hit area, but only “two minor injuries” have been reported, Crowley said.

Alicia Barcena, executive secretary of the U.N. Economic Commission for Latin America and the Caribbean, told reporters that the United Nations is sending satellite phones to Chile and is prepared to send 30 tons of food and other aid if the government needs it.

The earthquake, one of the largest ever recorded, hit southern Chile at the peak of the summer tourist season. The coastal community of Constitucion, home to 50,000 residents, was packed with tourists for “Noche Veneciana,” a summer festival, when the ground started to shake. Waves estimated at 30 feet drowned the town.

Residents scoured the wreckage on Monday in search of family members. Offshore, houses bobbed in the surf.

The scene was more chaotic elsewhere. In San Pedro de la Paz, a city next to Concepcion, looters stripped a clinic clean of medicine and supplies. Chilean National Television said there had been “neighbor versus neighbor” fighting in the coastal areas of Coronel and Lota, in Concepcion province. Food shortages were reported in many parts of the country, and electricity outages remained widespread.