The U.S. Geological Survey says a magnitude 6.8 earthquake has hit Ecuador. It's the second powerful quake of the day.

The USGS says the quake was below land about 15 miles (24 kilometers) north of the city of Rosa Zarate.

There were no immediate reports on the extent of damage or casualties.

Earlier a magnitude-6.7 earthquake struck Ecuador's coast, causing minor injuries and light damage in the same region where a 7.8 tremor killed more than 650 people last month.

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The quake overnight on Wednesday cut electricity in some coastal areas and sent people running into the streets as far away as the highland capital of Quito, witnesses said.

President Rafael Correa said the epicentre was the fishing village of Mompiche on the Pacific coast, about 368km from Quito.

"There are some light injuries because people ran out, or bumped into things," Correa said on state television, adding that there was also some minor damage, mainly to infrastructure already hit by the April disaster.

There was no tsunami warning.

The April 16 earthquake, Ecuador's worst in nearly seven decades, flattened buildings along the coast.

As well as the fatalities, it also injured more than 6000 people, left nearly 29,000 homeless, and caused an estimated US$2 billion (A$2.7 billion) in damage, according to the government's latest tally.

Correa described Wednesday's tremor as another aftershock from the April quake.

"Despite the alarm and the scare and the possibility of new damage ... it's normal, you expect aftershocks for two months after," he said.

-AAP