Guatemala's army has reached a remote village where dozens of houses were buried by mudslides triggered by Storm Eta's torrential rains.
President Alejandro Giammattei said around 100 people were feared dead in Quejá in the central region of Alta Verapaz.
Bad weather has hampered rescue efforts while roads are still blocked and large areas remain flooded.
Earlier, the authorities had confirmed at least 50 deaths across the country.
Eta made landfall in neighbouring Nicaragua on Tuesday as a Category Four hurricane with winds of 140mph (225km/h) and torrential rains. It then weakened into a tropical depression as it moved into neighbouring Honduras and later Guatemala.
President Giammattei said rescue efforts were limited by the country having only one helicopter adequate for these operations.
"We have a lot of people trapped [whom] we have not been able to reach," he said. A state of emergency has been declared in many areas.
The president described the situation in Queja as "critical". No bodies have yet been recovered from the area.
In neighbouring Honduras, at least 10 deaths have been confirmed, with hundreds of people reportedly waiting to be rescued from flooded areas.
Wendi Munguía Figueroa, 48, who lives in La Lima, a San Pedro Sula suburb, told the Associated Press: "We can't get off our houses' roofs because the water is up to our necks in the street."
On Twitter, Foreign Affairs Minister Lisandro Rosales said: "The destruction that Eta leaves us is enormous and public finances are at a critical moment because of Covid-19."
He added: "We make a call to the international community to accelerate the process of recovery and reconstruction."
On Friday, the storm was off Belize's coast and heading out to the Caribbean Sea, charting a course to Cuba and Florida this weekend, according to the US National Hurricane Center (NHC).