At least 30 people have died and thousands have been forced to evacuate their homes as storms and heavy rainfall continue to lash Central America, according to local officials, with the constant downpours flooding rivers, destroying homes, triggering landslides and cutting off entire communities.

Salvadoran authorities on Friday said the death toll had now reached 19, among them six children, while over 3,000 people remain in temporary shelters.

"We must save people's lives," Luis Amaya, who heads El Salvador's civil protection agency, told reporters Friday. "Material goods come and go, but now we must focus on protecting lives."

Guatemalan authorities on Friday reported 10 deaths, nearly 11,000 people evacuated, close to 380 still in temporary shelters, 300 severely damaged damage and four bridges destroyed.

Neighboring Honduras meanwhile reported 1 death and over 1,200 people evacuated - some 300 in the last 24 hours. They said the rains had cut off 180 communities and destroyed 22 houses.

In Mexico, authorities forecast strong rains across most of the country and torrential downpours across sections of the Pacific and Atlantic coasts, as well as further inland, bringing lightning, strong winds, possible hail and flooding around rivers.

The rains caused authorities to evacuate some 80 people from a children's hospital in Oaxaca state on Thursday, but also brought welcome replenishment to drought-hit reservoirs across the country, currently at around a third of their capacity.

Mexico's Conagua water authority warned of wind speeds of up to 70 kilometres per hour (44 mph) and waves of up 3 meters (10 ft) around the Gulf and Caribbean coasts. Equally strong winds on the Pacific side, it added, could cause possible tornadoes.

The rains were due to low-pressure channels interacting together across much of the country, as well as a monsoon trough drawing in moist ocean air from well into the North Pacific, the U.S. National Hurricane Center said, boosted by remnants of Alberto, the Atlantic hurricane season's first named tropical storm.

Alberto caused at least four deaths as it passed over north-east Mexico this week.

The U.S. National Hurricane Center predicted the heavy rainfall would continue through Friday across southern Mexico and northern Central America, bringing thunderstorms and showers as far south as Costa Rica and Panama into the weekend.