Tropical Storm Erika left at least 12 people dead in its wake when it swept over the island of Dominica on Friday then rolled on to pummel the Dominican Republic.

While crews rushed to search for survivors and clean up scenes of chaos on Caribbean islands, the US state of Florida declared a state of emergency.

Forecastasters expect the southeastern United States to feel Erika's wrath early next week, after it has lashed Hispaniola and the north coast of Cuba.

"I can confirm 12 but the number may be higher," Dominican Prime Minister Roosevelt Skerrit said, in a tweet posted on his way to the hard-hit village of Petite Savanne.

Local media, however, put the death toll much higher.

According to news site The Dominican.net, 27 people were reported dead in Petite Savanne alone after a "massive mudslide" demolished several houses.

Shaky aerial footage of Petite Savanne posted by Skerrit on Facebook showed what appeared to be a large river of dark brown mud descending down a foggy hillside.

"Regular access to Petite Savanne is totally cut off. Telecommunications are also not functioning over there," Skerrit tweeted.

Several injured people have been airlifted to hospital in the capital Roseau.

Skerrit also posted pictures showing swamped streets and beaches, a debris-filled air field and a road that collapsed, undercut by a torrent of water.

"I am asking residents to come out to help clean the streets, clear ravines and public buildings today," he tweeted.

Word of the death and destruction put the Dominican Republic on edge as it began to feel the effects of Erika later Friday.

"Tropical storm conditions are currently spreading across portions of the Dominican Republic," the National Hurricane Center said in its 1800 GMT update.

Earlier, in anticipation of what was to come, authorities issued a red alert, the country's highest.

Schools were closed and civil protection organizations were ordered to be at the ready so that, if necessary, they could quickly jump into action.

With unusually high waves expected, the Emergency Operations Center also closed beaches and banned vessels from leaving ports.

The Dominican Republic is particularly vulnerable to the impact of tropical storms due to the existence of rivers and streams in the capital Santo Domingo and elsewhere.

Packing maximum sustained winds of near 85 kilometers per hour (50 miles per hour), the storm could bring up to 10 inches (25 centimeters) of rain across parts of the Dominican Republic and Haiti, as well as Turks and Caicos and the southeastern and central Bahamas through Saturday, according to the NHC.

"These rains could cause life-threatening flash floods and mudslides," it warned.

In Puerto Rico, Erika left nearly 150,000 people without power, but appeared not to have caused major damage.

One possible silver lining: the rains could help ease a prolonged drought in the northern Caribbean.

The storm's approach also set off a scramble to prepare as far north as the US state of Florida, where the governor declared a state of emergency.

On its current trajectory, Erika could smack into southern part of the Sunshine State by early Monday, forecasters said.

"Tropical Storm Erika poses a severe threat to the entire state of Florida and requires that timely precautions are taken to protect the communities, critical infrastructure, and general welfare of this state," Governor Rick Scott said in declaring the state of emergency.

In Washington, White House spokesman Josh Earnest said President Barack Obama had been briefed about preparations for Erika's possible landfall in the United States.

The center of Erika was on track to move over the Dominican Republic and Haiti over the coming hours, then to pass Turks and Caicos and move on to the central and northwestern Bahamas on Saturday.