The agency gave the tremor an "orange alert" for potential "shaking-related fatalities," saying "significant casualties are likely and the disaster is potentially widespread."

"Past events with this alert level have required a regional or national level response," the USGS added. It also estimated damage and economic losses were possible.

Relatives of a CNN producer in the western port city of Guayaquil said they felt "very strong" tremors.

CNN afiliate Ecuavisa reported structural damage to buildings in Cuenca, one of the country's biggest cities. The historic city is in the UN list of world heritage sites.

There is no tsunami warning in effect for the area, according to the US National Weather Service.

The-CNN-Wire

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