Haiti hurried on Wednesday to prepare for incoming Tropical Storm Emily, urging evacuations ahead of the roiling system that could bring flash floods to the impoverished nation still struggling to recover from a devastating earthquake.

A tropical storm warning was in effect for Haiti as well as the neighboring island of Hispaniola, the Dominican Republic, and for the US territory of Puerto Rico, the US National Hurricane Center said.

Haiti's weather service chief Ronald Semelfort said heavy rains could start pounding the country late Wednesday, warning this "represents a great danger for the country still fragile from the January 2010 earthquake."

Tens of thousands of Haitians remain in makeshift camps more than 18 months after the quake, which killed an estimated 225,000 people.

Authorities were spreading the word and "are asking people in refugee camps... to evacuate vulnerable locations," said Haiti's civil defense chief Alta Jean-Baptiste.

"We will review this evacuation strategy based on the probability of damage from the storm," he added.

The Miami-based National Hurricane Center warned heavy rain from Emily could trigger deadly flash floods in Haiti, the Dominican Republic and Puerto Rico.

Emily is currently forecast to drop between four and six inches (10 to 15 centimeters) of rain on Hispaniola and Puerto Rico, "with isolated maximum amounts of 10 inches possible," the NHC said.

"These rains could cause life-threatening flash floods and mudslides in areas of mountainous terrain," the NHC said.

Haiti has in the past witnessed dozens of deadly landslides with many of the hills which surround the capital stripped bare of trees.

At 0600 GMT, Emily was some 220 miles (355 kilometers) southeast of Santo Domingo, packing winds of 50 miles per hour as it bore down on the island.

"Some slight strengthening possible before the center moves over the high terrain of Hispaniola," US forecasters cautioned.

The storm was moving towards the Dominican Republic and Haiti at 12 miles per hour, and on the forecast track its center "will be near the coast of Hispaniola on Wednesday," the NHC said.

The Dominican Republic declared an alert for portions of the country, called for mandatory evacuations in a dozen villages near dams and urged residents to take precautions in other areas.

"Residents in high-risk areas, who live next to rivers, streams and creeks... should take precautions and be aware of the recommendations of the relief agencies," the government's office of emergency services said.

A tropical storm watch was in effect for the US Virgin Islands, southeast Bahamas and the Turks and Caicos.

In the Pacific Ocean, meanwhile, Hurricane Eugene strengthened to a category three storm but still posed no threat to land, the weather service said.

At 0300 GMT, Eugene was around 580 miles (935 km) southwest of the southern tip of Baja California, moving west-northwest into open waters with sustained winds of 115 miles per hour.

The hurricane center said it may strengthen further Tuesday, but then should weaken as it moves over cooler waters.