(ABC NEWS) -- Nearly a million residents were forced to evacuate after a magnitude-8.2 earthquake struck off Chile's northern coast, triggering a small tsunami.
Six people are confirmed dead, Chilean Interior Minister Rodrigo Penailillo said; many of the victims died from heart attacks or falling debris.
The extent of the damage from Tuesday night's quake couldn't be fully assessed before daybreak,
President Michelle Bachelet said, but she wasn't taking any chances, declaring a state of emergency for the northern part of the country and deploying armed forces to prevent looting.
Military officials are also rounding up prisoners who escaped from a women's prison in the city of Iquique. Officials said 39 of the 300 prisoners who escaped have been recaptured.
Tsunami warnings have been canceled.
The quake, struck six miles beneath the ocean floor and 61 miles west-northwest of Iquique, triggered landslides that blocked roads, knocked out power for thousands, damaged an airport and provoked fires that destroyed several businesses. In Arica, another city close to the quake's offshore epicenter, hospitals treated minor injuries, and some homes made of adobe were destroyed, authorities said.
The earthquake was so strong that the shaking it caused in La Paz, Bolivia, 290 miles from the epicenter, was the equivalent of a 4.5-magnitude tremor, authorities there said. The quake triggered at least eight strong aftershocks in the first few hours, including a 6.2 tremor.
Bachelet's government extended its tsunami warnings for northernmost Chile long after they were lifted elsewhere. Its mandatory evacuation orders remained in effect until nearly dawn for coastal areas north of Antofogasta, a decision backed by the Pacific Tsunami Warning Center in Hawaii.
"We regard the coast line of Chile as still dangerous, so we're maintaining the warning," geophysicist Gerard Fryer said.
The currents should reach Hawaii at about 3:30 a.m. local time (9:30 a.m. ET today), Fryer said.
"All of our models are suggesting that it will be strong enough to generate significant currents. And therefore we are advising people to stay off the beach, stay out of the water," he said.
Bachelet, who just returned to the presidency three weeks ago, spoke well after midnight, five hours after the quake struck. 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, with 500 people dying.
"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 is one of the world's most earthquake-prone countries because the Nazca tectonic plate plunges just off the coast beneath the South American plate, pushing the towering Andes cordillera to ever-higher altitudes.
The latest activity began with a strong magnitude-6.7 quake March 16 that caused more than 100,000 people to briefly evacuate low-lying areas. Hundreds of smaller quakes have 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.
Mark Simons, a professor of geophysics at the California Institute of Technology, says historical records suggest that the region should anticipate an even bigger quake in the future.
"The key point here is that this magnitude-8.2 is not the large earthquake that we were expecting in this area," Simons said. "We're actually still expecting potentially an even larger earthquake.
"We expect about another 8.8, 8.9-magnitude earthquake here sometime in the future. It could be tomorrow, it could be in 50 years. We do not know when it's going to occur."
ABC News' Joshua Hoyos, ABC News Radio and The Associated Press contributed to this report.