Seven communities in already devastated areas were evacuated as the volcano's activity increased, with rescue operations halted.
In the city of Escuintla, near the summit, panicked locals rushed to their cars to escape, causing chaotic traffic.
An AFP photographer witnessed a large plume of ash rise into the sky, prompting an evacuation of everyone authorities could find before the police, the military and rescuers were stood down.
And a total of 192 people remain missing since the weekend eruptions, disaster relief agency chief Sergio Cabanas told reporters.
The search for bodies in mountain villages destroyed by the eruption was progressing slowly, officials said earlier, given the nature of the terrain and the way the volcano released large amounts of boiling mud, rock and ash down the mountain.
However, the prospects of finding any more survivors was poor, he said.
"If you are trapped in a pyroclastic flow, it's hard to come out of it alive," he said, adding that people who may have been caught in the flow may never be found.
The latest of the 73 victims was a 42-year-old woman who died in hospital having lost both legs and an arm in the eruption.
The 3,763-meter (12,346-foot) volcano erupted early Sunday, spewing out towering plumes of ash and a hail of fiery rock fragments with scalding mud.
Authorities said more than 1.7 million people had been affected by the disaster, including more than 3,000 ordered evacuated, many living in shelters in Escuintla, Sacatepequez and Chimaltenango since Sunday's eruption.
The speed of the eruption took locals by surprise, and could be explained by it producing pyroclastic flows, sudden emissions of gas and rock fragments, rather than lava, said volcanologist David Rothery of Britain's Open University.
President Jimmy Morales, who has declared three days of national mourning, has visited the disaster zone.
UN Secretary-General Antonio Guterres said he was deeply saddened by the "tragic loss of life and the significant damage caused by the eruption," and said the UN was ready to assist national rescue and relief efforts.
(Except for the headline, this story has not been edited by NDTV staff and is published from a syndicated feed.)
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