A series of earthquakes, including one of magnitude 6.6, struck in waters off the west coast of Mexico early on Sunday, but there were no immediate reports of any damage.
The 6.6 magnitude quake, which the U.S. Geological Survey initially reported at a magnitude of 6.8, struck at sea around 106 km (66 miles) southwest of Los Mochis, Sinaloa, at a depth of 10 km.
There were three other smaller quakes nearby, ranging in magnitude from 4.9 to 5.3.
"The biggest one felt reasonably strong, but there have been no reports of damage," an emergency services official said by telephone from Los Mochis, which is located in northern Sinaloa, and sits across the Gulf of California from the south of the Baja California peninsula.