The United States Geological Survey (USGS) said the quake had a preliminary magnitude of 7.4 and struck at 11:29 a.m. ET, 7 miles west of Santa María Zapotitlán, Mexico.
The temblor had a depth of about 20 miles and was centered along the Pacific coast of Oaxaca state near the resort of Huatulco.
The quake was felt in Guatemala and throughout south and central Mexico.
That threat passed about two hours after the initial quake, with the PTWC saying that waves of up to 2.2 feet were recorded in Acapulco and Salina Cruz.
"Minor sea level fluctuations of up to 0.3 meters above and below the normal tide may continue over the next few hours," the agency said.
Guatemala's national disaster agency issued a tsunami alert for its southern Pacific coast forecasting the arrival of waves up to a meter high. It advised people to move away from the sea.