An earthquake of magnitude 6.6 struck off the coast of El Salvador, 40 km south of La Libertad. (FILE)

An earthquake of magnitude 6.6 struck off the coast of El Salvador on Thursday, 40 km south of La Libertad, the U.S. Geological Survey said.

The U.S. National Tsunami Warning Center said there was no warning in place for the coast of the western United States.