The quake struck at a depth of 53 kilometers with an epicenter some 15 km southwest of Coquimbo, USGS said.
An elderly man and an elderly woman from Coquimbo suffered cardiac arrests as a result of the quake, police said, while there were several landslides reported on national highways.
The earthquake, which hit at 0132 GMT (Sunday), was felt in Valparaiso, O'Higgins and the region of the capital Santiago, as well as in Atacama and Coquimbo up north.
Thousands of homes lost power, which showed how intense the quake was, according to Ricardo Toro of the National Emergency Office.
Residents in Coquimbo and neighboring Serena, a coastal region about 500 kilometers from Santiago, evacuated to high ground even though authorities quickly ruled out a tsunami, according to local media.
The Coquimbo region experienced a tsunami in September 2015 after an 8.3 magnitude earthquake struck, killing a dozen people.