Authorities in northern Chile discovered surprisingly light damage and just six reported deaths Wednesday from a magnitude-8.2 quake — a remarkably low toll for such a powerful shift in the Earth's crust.

President Michelle Bachelet flew to the region to review damage in daylight after declaring a state of emergency and sending a military plane with 100 anti-riot police to join 300 soldiers who were deployed to prevent looting and round up escaped prisoners.

Thousands of people evacuated from low-lying areas were returning home after spending a long night outside due to the threat of a tsunami. The government's mandatory order to leave the coast was spread through cellphone text messages and Twitter, and reinforced by blaring sirens in neighbourhoods where people regularly practice earthquake drills.

Seawater flooded city streets and washed away some fishing boats in Iquique, but by early Wednesday no major tsunami damage was apparent. Chile's entire coast was initially subject to the mandatory evacuation order, which lasted nearly 10 hours in coastal communities closest to the offshore epicentre.

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The USGS says that the earthquake's centre was 10 kilometres beneath the ocean's surface and about 86 kilometres northwest of the mining port of Iquique. (CBC)

The shaking that began at 8:46 p.m. local time Tuesday also touched off landslides that blocked roads, knocked out power for thousands, damaged an airport and started fires that destroyed several businesses. Some homes made of adobe were destroyed in Arica, another city close to the quake's offshore epicentre.

Mining in Chile, which is the world's top copper producing nation, was not affected, although world prices for the red metal jumped as the quake raised supply concerns because most of the Chilean mining industry is in the northern regions.

About 300 inmates escaped from a women's prison in the city of Iquique, forcing the closure of the border with Peru. Officials said some two dozen had been captured early Wednesday.

500 died in 2010

Bachelet, who just returned to the presidency three weeks ago, spoke well after midnight, five hours after the quake struck and she flew to quake-hit regions on Wednesday morning to assess the damage. It was not lost on many Chileans that the last time she presided over a major quake, days before the end of her 2006-10 term, her emergency preparedness office prematurely waved off a tsunami danger. Most of the 500 dead from that magnitude-8.8 tremor survived the shaking, only to be caught in killer waves in a disaster that destroyed 220,000 homes and washed away large parts of many coastal communities.

"The country has done a good job of confronting the emergency. I call on everyone to stay calm and follow the authorities' instructions," Bachelet tweeted after Tuesday night's temblor.

Chile Earthquake

A fire burns at a restaurant after an earthquake in Iquique, Chile, on Tuesday. A powerful magnitude-8.2 earthquake struck off Chile's northern coast Tuesday night, killing at least 6 people. (Cristian Viveros/The Associated Press)

She put her interior minister in direct charge of co-ordinating the emergency response, announced that schools would be suspended in evacuated areas while authorities assessed the damage.

The only U.S. impact might be higher waves Wednesday for Hawaii's swimmers and surfers, the Pacific Tsunami Warning Center in Hawaii said.

20 aftershocks

The U.S. Geological Survey initially reported the quake at 8.0, but later upgraded the magnitude of the quake that struck 99 kilometres northwest of Iquique. More than 20 significant aftershocks followed, including one of magnitude 6.2.

The quake was so strong that the shaking experienced in Bolivia's capital, Sucre, about 470 kilometres away was the equivalent of a 4.5-magnitude tremor, authorities there said.

But Tuesday night's quake was not the big one seismologists are expecting.

APTOPIX Chile Earthquake

People embrace on the upper floor of an apartment building located a few blocks from the coast where they gathered to avoid a possible tsunami after an earthquake in Iquique, Chile, on Tuesday. (Cristian Viveros/The Associated Press)

"Could be tomorrow, could be in 50 years; we do not know when it's going to occur. But the key point here is that this magnitude-8.2 is not the large earthquake that we were expecting for this area. We're actually still expecting potentially an even larger earthquake," said Mike Simons, a seismologist at the Geological Survey.

Chile is one of the world's most earthquake-prone countries because just off the coast, the Nazca tectonic plate plunges beneath the South American plate, pushing the towering Andes cordillera to ever-higher altitudes. Nowhere along this fault is the pressure greater than in far northern Chile, an area known as the "Iquique seismic gap".

"This is the one remaining gap that hasn't had an earthquake in the last 140 years," said Simons. "We know these two plates come together at about 6, 7 centimetres a year, and if you multiply that by 140 years then the plates should have moved about 11 metres along the fault, and you can make an estimate of the size of earthquake we expect here."

The latest activity began with a strong magnitude-6.7 quake on March 16 that caused more than 100,000 people to briefly evacuate low-lying areas. Hundreds of smaller quakes followed in the weeks since, keeping people on edge as scientists said there was no way to tell if the unusual string of tremors was a harbinger of an impending disaster.