A shallow earthquake with a magnitude of 6.4 struck Ecuador's northwest coast on Sunday, in the region of April's deadly quake, the U.S. Geological Survey (USGS) said.

The quake was centered near the town of Esmeraldas, northwest of the capital, Quito, at a depth of about 35 km (22 miles), the USGS said. The Pacific Tsunami Warning Center did not issue a tsunami warning immediately after the quake.

The coastal region has been hit by a series of quakes since the April 7.8 tremor that killed more than 650 people, the nation's strongest quake in decades.

In May, two successive quakes measuring 6.7 and 6.8 in magnitude killed one person and caused minor damage.