Chilean authorities extended a curfew in the country's second-biggest city on Tuesday as troops struggled to contain worsening looting and crime in the wake of a devastating earthquake.

A night-time curfew in the badly damaged city of Concepcion was extended until midday after looters burned stores and residents complained of deteriorating security and slow government delivery of food and other basic supplies.

Despite the arrival of thousands of troops to reinforce local police, authorities were struggling to restore order in the city that bore the brunt of Saturday morning's 8.8-magnitude quake that killed at least 723 people.

Residents in Concepcion said they were organizing groups to defend their properties from robbers and looters, who the city's mayor said on Monday were becoming more organized.

Government help has been so slow to arrive, said Caroline Contreras, a 36-year-old teacher.

The soldiers just arrived and haven't been able to control the situation. The neighbors where I live are organizing to defend themselves because people are starting to rob houses.

President Michelle Bachelet, who condemned the pillage and criminality, dispatched 7,000 soldiers to the region and imposed curfews to restore order, saying her government was sending emergency food and medicine supplies.

The devastating quake struck as Latin America's most stable economy was trying to recover from a recession brought on by the global financial crisis. The total economic damage from the quake could exceed $15 billion, the catastrophe risk firm AIR Worldwide said.

But both the human and economic cost could have been a lot worse given the size of the quake, one of the world's biggest in the past century.

The government has acknowledged that it has battled to provide aid swiftly because of mangled roads and major power disruptions caused by the quake.

Residents also criticized the government's response in the battered central city of Talca, where the main hospital partly collapsed, forcing doctors and nurses to treat wounded quake victims in a clinic.

Counters overflowed with boxes of medicine that had been hastily arranged. Nearly 10 people have died at the hospital and the morgue has received at least 30 bodies, officials said.

We have not got any help from the government. We were expecting more and are still waiting for the three basics -- food, water and electricity, said 68-year-old Damian Vera Vergara.

Rescuers found signs of life on Monday in a collapsed apartment block in Concepcion. Workers heard knocking beneath the ruins of the 14-story building and were drilling into the rubble to try to reach the possible survivors. About 60 people were thought to have been killed when the block crumbled.

The quake sent massive waves surging into villages on the country's Pacific coast. In the town of Constitucion alone, 350 people were reported to have died, and the full scale of damage in isolated coastal towns remained unclear.

Fears of a major blow to Chile's economy from the quake receded somewhat as the stock market and the currency remained resilient. Other Latin American markets also took the quake in stride.

Mines in Chile, the world's leading copper producer, resumed activity and the central bank said it would keep interest rates at record lows to help stimulate the economy.

(Additional reporting by Terry Wade in Talca; Simon Gardner and Alonso Soto in Santiago; Writing by Stuart Grudgings; editing by Chris Wilson)

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