The epicenter was about 156 kilometers (97 miles) west of Guatemala City in the department of San Marcos, the Institute of Seismology said.
The tremor was felt across most of the country, including the capital, as well as in neighboring Mexico, according to Guatemala's National Coordinator for Disaster Reduction.
After reports of two deaths initially, three more people died of heart attacks sustained during the quake.
Video footage aired by rescue teams showed collapsed homes in western Guatemala, especially ones made of mud and straw in this poor Central American country.
Institute of Seismology spokesman Julio Sanchez said a 5.6-magnitude aftershock hit across the border in Mexico minutes after the quake.
In the southeastern Mexican state of Chiapas, 11 people were treated for injuries. Twenty houses and five schools were damaged, state officials said.
Guatemala is in a risk zone for tremors, located where the Caribbean Cocos tectonic plates converge with North America's tectonic plates.
San Marcos was hit by earthquakes in 2012 and 2014 that left dozens dead.
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