© Aliosha Marquez/APSoldiers guard the streets of Talcahuano, in southern Chile, after the earthquake.
Soldiers impose curfews and guard shops in attempt to control looters as death toll from disaster increases to more than 700

The Chilean military has taken control of towns and cities affected by the earthquake, it was reported today, imposing curfews and guarding shops from looters as the death toll from the disaster rose to more than 700.

The Chilean president, Michelle Bachelet, signed a decree putting the military in charge of security in the province of Concepción, where looters have targeted markets and supermarkets, hitting food and water supplies.

"We are facing a catastrophe of such unthinkable magnitude that it will require a giant effort [for Chile to recover]," Bachelet said after meeting ministers and generals at the quake-damaged La Moneda Palace.

Concerns are growing over Britons missing in the aftermath of the catastrophe.

An estimated 65,000 British people visit Chile each year, and a number of UK holidaymakers remain unaccounted for. A Foreign Office spokesman said there had been "no reports of any casualties" so far.

The Surfer's Cottage, an eco-cottage for surfers in Pichilemu, central Chile, listed five Britons among its missing.

UK charity workers were due to arrive in Chile today to help with aid efforts.

The US secretary of state, Hillary Clinton, will visit the country tomorrow on a previously scheduled trip unrelated to the quake.

"Our hemisphere comes together in times of crisis, and we will stand side by side with the people of Chile in this emergency," she said.

As aftershocks measuring up to 7.5 continued to batter the country, rescuers arrived at coastal cities to find that entire fishing villages had been washed away.

There were reports that 350 people had died in the town of Constitución, which was hit first by the earthquake and then by a tsunami.

The death toll was expected to rise dramatically because of the number of missing people. Identification of the dead has been hampered because most were sleeping when the quake struck and were not carrying any personal documents.

More than 100 people remained trapped inside a wrecked 14-storey building in Concepción, Chile's second largest city, 40 miles north-west of the epicentre.

The new building was only half occupied, but an estimated 20 bodies were removed from the rubble, and teams of firefighters were continuing to search the wreckage for signs of life.

An estimated 500,000 residential buildings have been severely damaged by the quake, leaving nearly one in eight residents homeless.

As food, water and fuel ran out, looting erupted in Concepción and police initially attempted to stop the looters using teargas.

A pitched battle erupted inside one supermarket, ending when police and supermarket officials allowed residents to remove essential items free of charge.

Food warehouses were also looted, and Jacqueline van Rysselberghe, the mayor of Concepción, warned: "We are going to have social explosion if aid is not received today."

The Chilean air force sent a 747 filled with police to the region in an attempt to regain control, while military roadblocks were set up outside some cities in an effort to prevent outsiders from joining the looting.

The cost of the quake damage was estimated to be $25-$30bn (£16-£20bn) by Eqecat, a firm based in Oakland, California, that specialises in disaster management software.

Experts at the company said Chile's history of major earthquakes and solid construction had been instrumental in preventing far more deaths, with building codes including earthquake-resistant standards in all new construction.

The Chilean president-elect, Sebastián Piñera, who takes office in less than two weeks, has worked closely with the outgoing Bachelet administration to organise long-term relief.

On Saturday, he asked key disaster relief and government officials to remain in office during the early part of his administration.

He also called for major sanctions against and investigations of construction companies involved in new housing projects that have collapsed.

Ricardo Ortega, the head of the Chilean air force, said yesterday a commercial airline service had been partially re-established and aircraft were now being allowed to land at Santiago's international airport.

With many major bridges destroyed and entire sections of Route 5, the main north-south highway, twisted and torn, delivery of relief aid to many areas has been made difficult and in some cases impossible.

Fears of a tsunami roaring across the Pacific Ocean were quelled yesterday when waves that hit Japan proved to be minimal.

Hundreds of thousands of people fled shorelines for higher ground after the Pacific Tsunami Warning Centre, based in Hawaii, warned 53 countries and territories that a tsunami was imminent.

After the centre lifted its warning, some countries kept their own watches in place.