(CNN) -- The eruption of a volcano in Guatemala was diminishing Friday, emergency officials said, though a heightened alert for the communities near the Volcan de Fuego remained in place.
As many as 35,000 residents had been evacuated because of the columns of ash and smoke that spewed from the "Fire Volcano," the Red Cross of Guatemala said.
The country's emergency management agency said the volcano's flow and ash had reduced since the beginning of the eruption. A government photo of Volcan de Fuego showed a massive wall of smoke that was lighter in color from where it rose into the sky, and dark gray as it drifted.
The average height of the column of smoke had decreased from about 2,000 meters (6,562 feet) to 700 meters, the agency said.
Still, civil protection authorities kept a heightened "orange" alert in place.
The volcano began spewing ash at 10 a.m. and was continuing to belch late in the afternoon near the country's former capital, Antigua, said Carmen Maria Caballero of the Guatemalan Red Cross.
CNN iReporter Harby David Marroquin had been working at a nearby golf course when he saw nature's pyrotechnics and shot video on his iPhone. It showed white smoke pouring out of the top of the 3,763-meter (12,346-foot) volcano.
Listening to the volcano gives him peace of mind, Marroquin said. "You feel an indescribable energy, and this time was no different."
Ten shelters, each able to house about 200 people, were opened in the affected villages, Caballero said. Most evacuees were staying with friends or relatives, she said.
Residents within 20 kilometers (12 miles) of the volcano were being taken from the affected zone in buses and private cars, she said. Ash was falling up to 40 kilometers (25 miles) from the volcano.
Several people were treated at mobile health centers for respiratory problems; one person was hospitalized in critical condition, according to Caballero.
Another Red Cross spokesman, Vinicio Sarazua Santillan, told CNN en Espanol that a number of people were remaining in their houses, unwilling to evacuate out of fear that their belongings could be stolen.
Thursday's eruption marked the sixth -- and the strongest -- this year, Caballero said. "It's a very active volcano," she added, but said that did not necessarily mean Thursday's eruption would last longer than others.
According to the Smithsonian National Museum of Natural History, the volcano is one of Central America's most active.