A tsunami alert in Chile and Peru was again issued, but was later lifted after waves of 2.4ft hit coastal areas.
Chile’s President Michelle Bachelet was among those evacuated on Thursday.
The quake is the strongest of several aftershocks following Tuesday’s tremor.
There have been no reports of damage from the latest quake.
The aftershock caused buildings to wobble and people to run into the streets in the port of Iquique, which was one of the cities hit by Tuesday night’s quake.
The latest quake was centered 14 miles south of Iquique.
The US Geological Survey (USGS) said the aftershock had a depth of 12 miles and was felt across the border in southern Peru, where people in the cities of Tacna and Arequipa also fled buildings.
President Michelle Bachelet had earlier praised the “calm behavior” of residents following Tuesday evening’s quake.
Nearly a million people were evacuated across the country after the authorities issued a tsunami warning.
“I think you have shown us all a tremendous example,” Michelle Bachelet said during a visit to the worst affected areas.
Michelle Bachelet declared northern provinces – Arica and Parinacota, and Tarapaca – disaster areas.
Tuesday’s quake struck at 20:46 local time 52 miles north-west of the city of Iquique, a mining area,
“We are here to recognize the calm behavior of the people of Iquique, who showed great civic responsibility, as did those of Arica,” said Michelle Bachelet.
Fires destroyed some businesses in the area and fishermen found their boats sunken and damaged in Iquique harbor.
Michelle Bachelet called on residents to “work together now” to repair the damage caused by the quake.
Waves of up to 6ft hit some areas.
Some 40,000 people in Tarapaca remain without power, said Ricardo Toro of Chile’s National Emergency Office (Onemi).
Hours after the first major earthquake, Chile’s army was deployed to Iquique after 293 inmates escaped from a women’s jail.
Ricardo Toro said that 131 had now returned voluntarily.
Chile is one of the most seismically active countries in the world.
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