A strong earthquake has hit off the coast of El Salvador, sending frightened residents running out of their homes in the predawn hours.

The U.S. Geological Survey says the quake had a preliminary magnitude of 6.6. Its epicenter was about 17 miles (28 kilometers) south-southeast of La Libertad, a suburb of the regional capital, Santa Tecla, and it was recorded at a depth of 65 kilometers (40 miles).

The earthquake was felt strongly in the capital, San Salvador, Thursday morning. People left their homes with flashlights, and power was knocked out in at least some areas.