A man covers up as Tropical Storm Agatha sweeps through Patulul, Guatemala on Saturday. (Moises Castillo/Associated Press)

More than 100,000 people have been evacuated from their homes and at least 99 are dead in Central America after the season's first tropical storm.

Torrential rain from Tropical Storm Agatha, which slammed into the region Saturday with wind speeds of up to 75 kilometres per hour, triggered landslides and floods across the region before weakening into a tropical depression and dissipating over the mountains of western Guatemala.

At least 82 of the dead are in Guatemala and word of damage and casualties is still filtering out of isolated areas.

Salvadoran President Maruricio Funes said nine people died in his country and Honduras reported eight deaths.

Although no longer even a tropical depression, Agatha still posed trouble for the region: remnants of the storm were expected to deliver 25 to 50 centimetres of rain over southeastern Mexico, Guatemala and parts of El Salvador, creating the possibility of "life-threatening flash floods and mudslides," the U.S. National Hurricane Center in Miami said in an advisory Sunday.

Agatha will continue to drop heavy rainfall across Central America over the next couple of days as it moves northeastward towards Florida. Some re-strengthening may take place and it is expected to affect the U.S. in the middle of the week.

Guatemalan President Alvaro Colom said Saturday night that the rivers in the country's south were flooding or close to it. Colom said 10.8 centimetres of rain had fallen in Guatemala City's valley in 12 hours, the most since 1949.

As of Saturday night, 4,300 people were in shelters and authorities said the number could rise as figures come in from around the country.

Earlier Saturday, Agatha's rains caused a landslide on a hillside settlement in Guatemala City that killed four people and left 11 missing, Guatemalan disaster relief spokesman David de Leon said. Most of the city was without electricity at nightfall, complicating search efforts.

'It rained in one day what it usually gets in a month.'— Cesar George of Guatemala's meteorological institute

Four children were killed by another mudslide in the town of Santa Catarina Pinula, about 10 kilometres outside the capital. And in Quetzaltenango, 200 kilometres west of Guatemala City, a boulder loosened by rains crushed a house, killing two children and two adults, de Leon said.

Calls to local radio stations told of many more landslides and possible deaths, but those reports could not be immediately confirmed.

A three-storey building in northern Guatemala City fell into a sinkhole but there were no reports of victims.

Cesar George of Guatemala's meteorological institute said the community of Champerico had received 30 centimetres of rain in 30 hours.

"It rained in one day what it usually gets in a month," George said.

Colom said authorities have not been able to reach Champerico by "air, land or sea."

Rain causes landslides in El Salvador

In El Salvador, President Mauricio Funes declared a "red alert," the highest level of emergency, after rains delivered by Agatha triggered at least 140 landslides throughout the country and killed two adults and a 10-year-old child.

Civil defence officials said the Acelhuate River that passes through the capital, San Salvador, had risen to dangerous levels and was threatening to overflow into city streets.

In Honduras, national emergency agency Copeco reported one man was crushed to death by a wall that collapsed in the town of Santa Ana, near the capital, Tegucigalpa.

Flooding and slides destroyed 45 homes in the country and prompted authorities to evacuate 1,500 people, according to figures released by the agency.

Agatha formed as a tropical storm early Saturday in the East Pacific.

Before the rains, Guatemala already was contending with heavy eruptions from its Pacaya volcano that blanketed the capital in ash and destroyed 800 homes.

The volcano, which is just south of the capital, started spewing lava and rocks Thursday afternoon, forcing the closure of Guatemala City's international airport. A TV reporter was killed by a shower of burning rocks.