Emergency workers in Guatemala, Honduras and El Salvador are struggling to get aid to communities cut off by Tropical Storm Agatha.
The storm has left at least 150 people dead since Saturday, most of them in Guatemala.
Rescuers are digging through mud and rubble in search of dozens of people still missing after landslides destroyed entire communities.
The storm has passed but officials warn that swollen rivers still pose a risk.
The Guatemalan authorities said 123 people were known to have died, while in Honduras 14 people were killed, and nine in El Salvador.
All three countries have declared emergencies in an attempt to increase immediate aid and resources.
The storm dumped more than 3ft (1m) of rain on parts of Guatemala, the government said, causing rivers to burst their banks and hillsides to collapse.
In the capital, Guatemala City, a giant sinkhole opened up, reportedly swallowing a couple of buildings.
Officials initially said the storm was to blame, but now say they will carry out further studies to determine the exact cause, as a sinkhole appeared in the same area in 2007.
Tens of thousands of people are living in temporary shelters, either because their homes were destroyed or because they were evacuated from areas at risk of flooding.
Roads and bridges have been smashed, making it difficult to get aid to the worst-hit areas.
Guatemala's main airport is still closed to commercial flights because of the eruption of the Pacaya volcano last week, slowing the arrival of international help.
The storm has broken up but further rain is forecast for the coming days.
El Salvador's President, Mauricio Funes, said the risk of further destruction was still high.
"It has rained so much that the glass is full and one more drop could be fatal," he said.
Authorities there said most of the countries roads had been affected by landslides.