The northwestern province of Esmeraldas -- hit hard by a devastating temblor in April -- bore the brunt of the new quake, too.
Three people died and 47 were injured as a result of the quake, according to disaster management agency SGR. At least 700 families had to leave their homes.
The dead all suffered from heart attacks, said President Rafael Correa, who rushed to Esmeraldas.
The quake caused a lot of damage to resort facilities in the coastal towns of Atacames and Tonsupa, and many homes also collapsed, Rivera told Radio Publica.
The quake struck in the Pacific off Atacames and was followed by aftershocks registering as high as 4.2, the Geophysical Institute reported.
It said the earthquake hit 5.7 after first reporting its magnitude was 5.8.
The quakes knocked out electricity in several areas of Esmeraldas but power was later restored. Schools were closed and it was unclear when they would reopen.
The capital city of Esmeraldas, which has the same name, is home to the country's main oil refinery, a power plant, two oil pipelines and an oil export port. But no damage to these facilities was reported, the government said.
The South American nation is still recovering from a devastating 7.8-magnitude quake that killed 673 people in April and left some 6,000 injured.
That quake flattened homes and buildings up and down a long stretch of Ecuador's coast, reducing picturesque resort towns to rubble.
