There was no damage, and no injuries or casualties were reported, according to a spokesman for the government's disaster response office.
The quake's epicentre was located 79.7 kilometres (50 miles) south of Guatemala City, and it occurred at 7:09 am (1309 GMT).
Guatemala is in a risk zone for tremors, as it is located where the Caribbean Cocos tectonic plates converge with North America's tectonic plates.
In 2012 and 2014, the department of San Marcos was hit by two earthquakes that left dozens dead.