"Not everyone escaped, I think they were buried," Hernandez said in a video released by CONRED, the government agency for disaster reduction. "We saw the lava was pouring through the corn fields, and we ran toward a hill."
Guatemala's President Jimmy Morales has declared three days of national mourning.
1.7 million people affected
More than 3,100 people have been evacuated and 1.7 million people have been affected by the eruption, according to CONRED.
Satellite footage of Fuego shows the massive dark gray eruption was visible even from space.
Authorities urged residents living near the volcano to evacuate immediately, and warned some in Chimaltenango, Sacatepequez and Escuintla states to watch out for volcanic rocks and ash.
Residents were told to avoid roads close to the volcano and make sure water is not contaminated.
The eruption officially ended late Sunday, said Guatemala's National Institute of Seismology, Vulcanology, Meteorology and Hydrology.
"The eruption ... is reaching its end with 14.763 feet of ash and weak-to-moderate explosions and incandescence in its crater," it said in a statement.
But it warned there could be new eruptions, and residents in the surrounding areas should be on alert for mudslides containing volcanic material.
Why this eruption is much deadlier than Hawaii's
The Guatemala eruption stirred recent memories of Hawaii's Kilauea eruption, which terrorized Big Island on May 3.
But the Fuego eruption is much deadlier -- for several reasons.
Pyroclastic flows can race down a volcano at hundreds of kilometers per hour -- much faster than people or even cars.
To make matters worse in Guatemala, "villages are right on the foothills of the mountain," CNN meteorologist Ivan Cabrera said. "So they had no time (to escape)."
'Ring of fire'
The 40,000-kilometer (25,000-mile) area stretches from the boundary of the Pacific Plate and the smaller plates such as the Philippine Sea plate to the Cocos and Nazca Plates that line the edge of the Pacific Ocean.
Volcan de Fuego, which means fire volcano, is one of Central America's most active.
It is near the colonial city of Antigua. Sunday's explosion rained soot over the popular tourist destination and other villages in the Sacatepéquez state, covering them in ash.
Villages south of the volcano in the Escuintla department were affected, too, Cabañas said. Some ash reached the capital of Guatemala City about 25 miles away, forcing the closure of its international airport. The Guatemalan army shared images of officers clearing the runway with push brooms.
Mexican President Enrique Peña Nieto expressed condolences and offered assistance.
"All our solidarity and support to the President Jimmy Morales and the Guatemalan people for the loss of human life after the eruption of the volcano of Fire."