(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.
"For the moment, all that are seen are weak and moderate explosions as well as flows of lava that also diminished in length," the government said on its website, citing the National Institute of Seismology, Volcanology, Meteorology and Hydrology.
"People are returning to their houses now that the activity has lowered," said David de Leon, a spokesman for CONRED Guatemala, which organizes disaster relief. But, he added, "We tell them it might be necessary" to leave again, should the volcano's activity spike.
Though 35,000 people might theoretically have been affected by the columns of ash and smoke that rose from the "Fire Volcano," only 5,000 live southwest of it, the direction that was threatened, he said.
On Thursday night, only about 800 people sought refuge at the four shelters set up by the Red Cross, said a Red Cross spokesman, Vinicio Sarazua Santillan. "Many of the people who were evacuated decided to go back to their houses, and others never left," he said.
He predicted that the shelters would be empty Friday night "if the volcano continues in tranquility."
Sarazua said that a number of people refused to evacuate out of fear that their belongings could be stolen. But, he said, as of Friday afternoon he had heard no reports of looting.
De Leon said he also had heard no reports of looting.
A government photo of Volcan de Fuego showed a massive wall of smoke that was lighter 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 (6,560 feet) to 700 meters, the agency said.
Still, civil protection authorities kept in place the heightened "orange" alert.
The volcano began spewing ash at 10 a.m. Thursday 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."
Three people were treated at mobile health centers for respiratory problems, according to de Leon.
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.