He said on radio a river of lava has overwhelmed a village.
At least seven people have been killed from Volcan de Fuego's devastation.
Volcan de Fuego, which translates to "volano of fire" exploded just before noon on Sunday, 27 miles from Guatemala City.
One video published by news outlet Telediario purportedly taken in the El Rodeo village showed three bodies strewn atop a lava flow, as rescuers arrived to attend to an elderly man caked from head to toe in ash and mud.
A river of lava destroyed homes and burnt people inside as the Fuego volcano pumped black smoke into skies southwest of Guatemala City this morning. "I think they ended up buried", Consuelo Hernandez, a resident of the village of El Rodeo, told the newspaper Diario de Centroamerica.
Some 3,100 people evacuated nearby communities, and the eruption was affecting an area with a population of about 1.7 million people. "Where we saw the lava fall, we ran to a hillside" to escape, she added.
"The toll was 25 dead as of 9:00 pm (0300 GMT)", the spokesman for the National Coordinator for Disaster Reduction (CONRED) said in a WhatsApp group.
Around four hours after the explosion lava flows reaching temperatures of about 1,300degrees Fahrenheit, cascaded down the mountain, according to ABC.
The seventh victim of the frightening natural disaster was found in the streets of El Rodeo before they later died in an ambulance.
Ash has fallen into the nation's capital, Guatemala City, in addition to regions of Sacatepequez, Chimaltenango and Escuintla.
It was the 3,763-metre volcano's second eruption this year. Lesser amounts of ash reached the capital of Guatemala City some 25 miles away, forcing the closure of its worldwide airport, CONRED said.
The conical Volcan de Fuego is 12,346 feet above sea level at its peak.