Chilean troops are heading to the country's devastated earthquake zone as reports emerge of desperate survivors turning to looting and arson, BBC reported.
President Michelle Bachelet said a total of 7,000 troops would soon be in place in areas around Concepcion, the city closest to the epicentre.
An air bridge has been set up between Santiago and Concepcion, with 100 tons of food aid due in the next few hours.
At least 723 people have been confirmed dead in the 8.8-magnitude quake.
Ms Bachelet said reinforcements would join the troops already in the provinces of Bio Bio and Maule, bringing the total to some 7,000.
Concepcion is under another night under curfew, which has been extended to be in force from 2000 (2300 GMT) until noon on Tuesday.
Reports are emerging from the city of residents clashing with police as they lay siege to shops and supermarkets in the search for food.
The army was called in to help the police force deal with looters, some of whom filled shopping trolleys with groceries while others made off with plasma TVs and other electrical appliances.
Some 160 people were arrested for looting and breaking the curfew, police said on Monday.
Clashes with looters saw one 22-year-old man shot and killed.
And by Monday evening tensions had flared once more, with troops deployed to the streets after a blaze began in a looted supermarket.
Chilean newspaper La Tercera reported that despite the presence of troops, a huge fire was intentionally started at a building housing the Polar department store.
The blaze caused the building to collapse, La Tercera reported. Marco Riquelme, a regional spokesman for the department store, told La Tercera the incident was a "clear example" of the "chaotic situation" survivors were enduring in Concepcion.
Hospital set to collapse
Reports are beginning to emerge of the scale of the devastation in areas south of the Chilean capital, Santiago.
A BBC team that reached the town of Curico, between Santiago and Concepcion, said 90% of the town historic centre had been damaged.
The town's Mayor, Hugo Rey Martinez, told the BBC's Will Grant the hospital building was compromised and would soon collapse.
However, food and water was being distributed and the situation was comparatively calm, our reporters said.
In coastal towns and villages hit by giant waves after the earthquake, the scale of destruction is becoming clear.
More than 300 bodies were reportedly found in the fishing village of Constitucion alone. The mayor of Constitucion said the town's seafront and centre had been "completely destroyed".
In the port of Talcahuano, more than 20 boats were swept ashore and dumped in the streets by the waves.
Relief efforts are beginning to get under way, with the United Nations pledging to send aid quickly to the earthquake zone.
Many of Concepcion's 500,000 inhabitants are short of food and have seen their water and electricity supplies cut off.
UN spokeswoman Elisabeth Byrs said Chile had requested field hospitals with surgery facilities, mobile bridges, communications equipment, kitchens, and disaster assessment and co-ordination teams.
However, the domestic aid effort suffered a setback when a small plane carrying six people near Concepcion, killing all those on board.
The small Chilean plane, which was carrying an aid and assessment team to Concepcion, crashed close to the nearby town of Tome on Monday afternoon, local media reported.
About two million Chileans are believed to have been affected by Saturday's earthquake, the seventh most powerful on record and the worst disaster to befall Chile in 50 years.
The epicentre of the quake was 115km (70 miles) north-east of Concepcion and 325km (200 miles) south-west of the capital Santiago.
About 1.5 million homes in Chile have been damaged. Most of the collapsed buildings were of older design - including many historic structures.
One US risk assessor, Eqecat, has put the cost of repairing the damage at between $15bn and $30bn (£9.8bn - £19.6bn) or 10-20% of the country's gross domestic product.
US Secretary of State Hillary Clinton would visit Santiago on Tuesday and meet Ms Bachelet and Mr Pinera, officials said.
The European Union has pledged 3m euros ($4m; £2.7m) in emergency aid for Chile. Japan said it was providing an emergency grant of $3m, as well as sending tents, generators, water cleaners and other emergency gear, while China has pledged $1m.