A 6.4 magnitude earthquake struck Saturday off the coast of Mexico in the Gulf of California, posing a risk of local tsunamis, US seismologists said. \"Earthquakes of this size sometimes generate local tsunamis that can be destructive along coasts located within a hundred kilometers of the earthquake epicenter,\" the Pacific Tsunami Warning Center said in a bulletin. \"Authorities in the region of the epicenter should be aware of this possibility and take appropriate action,\" it said. There were no immediate reports of damage or casualties in the area of the quake, whose epicenter was about 74 kilometers (46 miles) southwest of Etchoropo, Mexico. The US Geological Survey initially reported that the quake had a magnitude of 6.8 but downgraded it to 6.4 on moment magnitude scale. The agency said the quake struck in the Gulf of California at 1755 GMT at a depth of about 10 kilometers (6.2 miles.) The Hawaii-based Pacific Tsunami Warning Center said there was no threat of a \"destructive widespread tsunami.\"