Mobs of angry, hungry survivors of the huge Chile earthquake have set fire to shops in the devastated city of Concepcion as troops battle to keep order.

The death toll rose to 723 and security fears ballooned ahead of a Tuesday visit by US Secretary of State Hillary Clinton with a promise of aid after the magnitude 8.8 quake and tsunami that hit seaside resorts and villages.

Huge flames and clouds of black smoke billowed out over Chile's second city as rescue teams picked through the debris trying to reach survivors whose anguished cries could be heard in the rubble.

One person was killed as troops and police clamped down on rampant looting, making 160 arrests, Deputy Interior Minister Patricio Rosende said. Violence was also reported in other towns in the quake zone.

President Michelle Bachelet said there would be 7,000 troops in the zone by Tuesday. Alongside the troops, aid pledges also rolled in from around the world, with the European Union offering four million dollars, Japan three million and China one million.

The UN's humanitarian coordination office (OCHA)

said Chile had asked for field hospitals, mobile bridges, communications equipment and disaster assessment teams.

After touring the disaster zone, President-elect Sebastian Pinera said "the situation is worse than expected" and recounted hearing cries for help when he entered a collapsed building not yet reached by rescuers.

Teams with heat sensors and sniffer dogs picked through the debris of shattered buildings in Concepcion and special cameras showed three, perhaps four, survivors trapped in the twisted ruins of a 15-story apartment block.

"We'll have to work with the precision of watchmakers,” said fire chief Juan Carlos Subercaseaux. "May God help us."

Some two million people, an eighth of Chile's population, are said to be affected by the quake.

Injured people slept out for a third night, still rattled by aftershocks. More than 120 tremors with a magnitude greater than 5.0 have struck Chile since Saturday's quake -- one of the most powerful ever recorded — including a 5.5 temblor before dawn Tuesday.