(CNN) Guatemala's Fuego volcano erupted, killing at least 25 people and leaving residents covered in ash as they fled from billowing plumes.

The volcanic eruption Sunday spewed a river of red hot lava and belched thick clouds of smoke nearly six miles into the air, according to the CONRED, the government agency for disaster reduction. Ashen remnants covered neighborhoods.

In addition to the fatalities, 20 others were injured, CONRED said.

Survivors described the horror and destruction when the volcano erupted.

"Not everyone escaped, I think they were buried," Consuelo Hernandez said in a video released by CONRED. "We saw the lava was pouring through the corn fields and we ran toward a hill."

Hernandez told officials from the disaster agency that some of her relatives were buried. Images from the scene showed a firefighter weeping.

Guatemala's President Jimmy Morales declared three days of national mourning.

A rescue worker carries a girl in El Rodeo, Escuintla.

Evacuate immediately

More than 3,100 people have been evacuated while search and rescue efforts continue into the night, said Sergio García Cabañas, director of the disaster agency. The explosion will affect 1.7 million people.

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 ensure water is not contaminated.

At least 15 people have been hospitalized, including 12 children, some of whom suffered severe burns, the health ministry said.

The eruption officially ended late Sunday, according to the 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. Volcanic ash had spread in a 12-mile radius and winds could carry the cloud even farther, officials said.

Neighbors stand outside a temporary morgue near Volcan de Fuego in Alotenango, Guatemala.

'Ring of fire

Guatemala is situated on the "Ring of Fire," an area of intense seismic activity.

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."

The President of El Salvador offered his condolences via Twitter and said his country stood ready to assist its neighbor.

Israel's Ambassador to Guatemala and the Mayor of Puerto Rico also expressed their solidarity.