The U.S. Geological Survey says the quake had a preliminary magnitude of 6.6. Its epicenter was about 17 miles 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.
At least seven aftershocks of between magnitude 4.1 and 5.0 were recorded, while El Salvador's Ministry of Environment and Natural Resources warned of a possible tsunami and advised people to stay away from the Pacific Ocean for the next four hours.