'Out of control'
In the hard-hit city of Concepcion, about 500km south of the capital, Santiago, at least 100 people were feared trapped in the rubble of a collapsed apartment block where rescue workers dug through the night to find survivors.
"We spent the whole night working, smashing through walls to find survivors," Marcelo Plaza, a Chilean commander and rescue worker, said.
"The biggest problem is fuel, we need fuel for our machinery and water for our people."
Television images showed residents carting food and electronics from damaged stores
Meanwhile, security officials used tear gas and water cannons to disperse crowds of looters who took food and electrical appliances from a supermarket in the city.
Television images showed people carting groceries and other foods from ransacked stores as police looked on.
Other residents looted pharmacies and a collapsed grain silo, hauling off bags of wheat, television images showed.
Jacqueline van Rysselberghe, the mayor of Concepcion, said the situation was getting "out of control" due to shortages of basic supplies.
But she warned that the looting was "totally unjustifiable".
"We've got a very complicated situation and the people feel very vulnerable," she told local radio.
'State of catastrophe'
Earlier, Bachelet said 1.5 million people had been affected by the earthquake and she declared a "state of catastrophe",saying that officials were still trying to evaluate the "enormous quantity of damage."
Meanwhile, officials in her administration said 500,000 homes were severely damaged.
The earthquake has raised a daunting first challenge for Sebastian Pinera, who was elected Chile's president in January and who takes office in two weeks.
"Unfortunately, Chile is a country of catastrophes," Pinera said.
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He said the disaster heavily damaged many of the country's roads, airports and ports.
Saturday's quake also triggered a tsunami that killed at least four people on Chile's Juan Fernandez islands and caused serious damage to the port town of Talcahuano.
More than 60 aftershocks of magnitude 5 or greater were reported in the hours after the quake.
The US Geological Survey (USGS) said the earthquake struck 92km northeast of Concepcion at a depth of 63km at 3:34am local time (06:43 GMT) on Saturday.
Aid organisations and government officials in Britain and the US have offered to help Chileans in their efforts to rebuild their country.
Barack Obama, the US president, has said the US has resources in position to deploy should the Chilean government ask for help following the earthquake.