The government's ECU 911 safety service said there were no major incidents and a tsunami had been ruled out.
The USGS said the quake's epicentre was 55 miles (88.5 km)northwest of Portoviejo at a depth of 6.2 miles (10 km) below the Pacific seabed. The quake, initially reported as a magnitude 6.1, struck at 5:29 p.m. (2229 GMT).
Last year, a devastating 7.8-magnitude earthquake struck Ecuador's Pacific coast in April, killing more than 650 people.
(Reporting by Alexandra Valencia in Quito and Sandra Maler in Washington; Writing by Brian Ellsworth and Girish Gupta; Editing by Bill Trott and Sandra Maler)
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