Heavy rain from the remnants of Hurricane Felix has been falling in Honduras and Nicaragua, threatening to trigger flooding and mudslides.
The Honduran city of La Ceiba has already been flooded
The storm has weakened as it passes over land but US forecasters warn the rain could produce "life-threatening" flash floods.
Hurricane Felix hit land in north-east Nicaragua on Tuesday as a category-five hurricane - the maximum strength.
Nicaraguan authorities have declared the region a disaster zone.
Meanwhile, another hurricane, Henriette, is moving north across Mexico's mainland after hitting the Baja peninsula on Tuesday, amid warnings from forecasters that it could provoke flooding.
At least seven people were reported to have been killed as Henriette struck Mexico's Pacific coast.
Felix has now faded to a tropical depression but the US National Hurricane Center in Miami warned up to 25 inches (64 cm) could fall in some mountainous areas of Central America.
Many buildings along Nicaragua's Miskito coast have been damaged
Some 20,000 people in dangerous areas in Honduras have been taken to safer ground.
The Honduran capital, Tegucigalpa, which is prone to flooding, was on alert on Wednesday with people rushing to stock up on supplies.
"Here it rains for two hours and the city floods. They're saying it could rain for 18 hours and we're preparing for the worst," the city's mayor Ricardo Alvarez told Reuters news agency.
Felix has revived memories of Hurricane Mitch which in 1998 killed more than 10,000 people, many of them in Honduras.
Nicaraguan authorities have been airlifting supplies to the north-eastern Caribbean region, which bore the brunt of the storm and where at least four people were reported to have died.
Nicaraguan media said many villages along the Miskito coast had been devastated.
Officials said some 90% of the infrastructure in Puerto Cabezas, the region's main town, had been damaged.
Power lines and trees were blown down, and the town's hospital has been flooded.
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