A magnitude 5.4 earthquake struck Mexico's southern coast Monday, with shaking felt as far as Mexico City.The quake struck at 1:15 p.m. about six miles south of Cuajinicuilapa, Mexico, near the border of the Oaxaca and Guerrero states, according to the USGS.There were no immediate reports of damage but there were reports of buildings swaying in Mexico City more than 300 miles from the epicenter.