At least 192 people are reportedly missing and 75 are dead as a result of the explosion of the Fuego volcano in Guatemala on Sunday, officials say.
Villages on the slopes were buried in volcanic ash and mud.
Rescue work on Tuesday was disrupted when a new eruption sent hot gas and molten rock streaming down the volcano's south side.
More than 1.7 million people have been affected by Sunday's eruption, with more than 3,000 evacuated.
Tuesday's explosion took many by surprise after volcanologists said the eruption, which had sent ash up to 10km (33,000ft) into the sky on Sunday, was over for the near future.
Eddy Sanchez, the head of Guatemala's National Institute of Seismology, had predicted "no imminent eruption over the next few days".
Boris Rodriguez has no-one to turn to now. He lost more loved ones in a single night on Sunday than many do in a lifetime.
Mr Rodriguez's wife, both of her parents, his brother and sister-in-law and their children died when the Fuego volcano erupted.
"I saw the children's bodies," he told me between sobs. "They were huddled together in the bed, like they were trying to hide from what was happening."
If Mr Rodriguez, who is 25, were a solitary case, it would be heartbreaking enough. But most of his neighbours in the village of El Rodeo have similar stories of grief. The village was almost entirely wiped off the map.
Almost 200 people remain unaccounted for, according to an international news agency, quoting Guatemala's Disaster Relief Agency.
No evacuation alert was issued before the volcano erupted on Sunday, said the agency's chief, Sergio Cabañas.
He added that local residents had received training in emergency procedures but were not able to act because the initial volcanic activity happened too fast.
Sunday's blast generated pyroclastic flows - fast-moving mixtures of very hot gas and volcanic matter - which descended down the slopes, engulfing communities including El Rodeo and San Miguel Los Lotes.
Volcanologist Dr Janine Krippner told that people should not underestimate the risk from pyroclastic flows and volcanic mudflows, known as lahars.
"Fuego is a very active volcano. It has deposited quite a bit of loose volcanic material and it is also in a rain-heavy area, so when heavy rains hit the volcano that is going to be washing the deposits away into these mudflows which carry a lot of debris and rock.
"They are extremely dangerous and deadly as well."
The speed it travels depends on several factors, such as the output rate of the volcano and the gradient of its slope. But they have been known to reach speeds of up to 700km/h - close to the cruising speed of a long-distance commercial passenger aircraft.
In addition, the gas and rock within a flow are heated to extreme temperatures, ranging between 200C and 700C. If you're directly in its path, there is little chance of escape.
The eruption of Vesuvius, in Italy, in 79 AD produced a powerful pyroclastic flow, burying the Roman towns of Pompeii and Herculaneum under a thick blanket of ash, reports BBC.
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