He has urged residents to not leave their homes unless their was an urgent need to.
A spokesman for Guatemala's disaster agency said television reporter Anibal Archila was killed after being hit by a shower of rocks spewed from the volcano.
|Two to three inches of ash accumulated on streets in parts of Guatemala City [AFP]
The spokesman also said three children, aged between seven and 12 years old, have gone missing.
Brenda Castaneda, a resident of the southern village of Calderas, said: "We thought we wouldn't survive. Our houses crumbled and we've lost everything."
Two to three inches of ash accumulated on streets in some parts of the city, and authorities imposed limits on trucks and motorcycles to help speed up traffic.
Eddy Sanchez, the head of Guatemala's seismological institute, warned another eruption could take place "in the coming days" at Pacaya, the most active volcano in Central America.
Sanchez said the volcano has accumulated a lot of energy over several years.
"Like a pressure cooker, it will release the pressure violently," he told reporters.