Thousands more troops deployed across Chile yesterday as armed vigilantes patrolled neighbourhoods to ward off looters and protect residents already traumatised by a devastating earthquake.

"The thugs have taken over the city. Now we are not afraid of the earthquakes, we're afraid of the criminals," Marcelo Rivera, the mayor of Hualpen, said on a Chilean radio station.

President Michelle Bachelet doubled the number of troops patrolling the worst-hit areas to 14,000, as people in the second largest city of Concepcion were slapped with an 18-hour curfew.

"Military personnel will be present in the streets of Concepcion until midday to maintain public order, and they will not waver in carrying out their duties," warned General Guillermo Ramirez.

A similar curfew was also imposed on three other towns badly damaged by Saturday's 8.8-magnitude quake, which was so strong it triggered a Pacific-wide tsunami and according to a Nasa scientist probably shifted the earth's axis.

The curfew, unprecedented since the end of the 17-year dictatorship of General Augusto Pinochet, is likely to trigger concern in the South American country.

But Ms Bachelet defended her government's handling of the crisis as the first aid supplies began trickling into the quake-hit areas.

"We understand your urgent suffering, but we also know that these are criminal acts that will not be tolerated," Ms Bachelet said.

Officially, the quake killed almost 800 people, but the death toll looks set to rise sharply as relief teams reach more isolated areas.

"The tsunami affected 200 kilometres of coastline, at places sweeping 2,000 meters inland," General Bosco Pesse, who is running emergency operations in the Maule region of a quarter million people, said.

"Some 600 people died in this area, but the toll could climb to 1,000."

In Concepcion, some 500 kilometres south of Santiago, hungry, desperate residents roamed the streets looking for food and water.

Across many neighbourhoods, people were taking matters into their own hands, organising self-defence groups, barricading streets and preventing strangers from entering.

Ms Bachelet, outraged at the vandalism after stores were looted and torched, said it was not acceptable that "people have to organise mechanisms for their self-defence, just to hold onto the few possessions that they still have after the earthquake."

Hualpen mayor Rivera urged the government to send in a contingent of troops, and grimly warned: "If they have to kill, then let them kill."

US Secretary of State Hillary Clinton arrived in Santiago yesterday carrying communications equipment and said the US stood ready to help.

Santiago, mostly built to strict earthquake codes, escaped the worst of the damage. But as journalists and aid workers slowly trekked across damaged roads, the extent of the quake was gradually coming to light.

Two million people, or one-eighth of the population, are said to have been affected.

The temblor razed street after street of homes in the old heart of Talac where entire suburbs are now sleeping rough.

"We're scared, there are bad people about, so we do guard duty through the night," said Mario Saabedra, 76, whose wife suffered a diabetic attack in the early hours but refused to go to hospital.

"We have no food or water, and no one, but no one, has come to check on us," he said.

There is little to no electricity, water supplies are slowly returning for the 200,000 residents, and most shops remain closed.