Hurricane Dorian is heading on Wednesday toward Puerto Rico and could take aim at the southeastern United States over the weekend with a potentially higher intensity, the National Hurricane Center (NHC) said Wednesday.

The NHC said in its 1800 GMT public advisory that the storm was near St. Thomas, US Virgin Islands, and moving northwest at 20 kph (13 mph).

The Category 1 hurricane has maximum sustained winds of 120 kph (75 mph), the NHC said.

"On this track, Dorian should continue to move near or over the US and British Virgin Islands this afternoon and then move over the open Atlantic well east of the southeastern Bahamas," the NHC said.

A hurricane warning is in effect for Vieques and Culebra, Puerto Rico, the US Virgin Islands and the British Virgin Islands.

The NHC has issued both a hurricane watch and a tropical storm warning for Puerto Rico.

The tropical storm watch for the Dominican Republic has been discontinued, the NHC said.

"Dorian is forecast to continue strengthening during the next few days over the Atlantic waters," hurricane forecasters said.

Forecasters said the storm was intensifying as it moved toward Puerto Rico.

"Hurricane conditions are ongoing over portions of the US Virgin Islands, and are expected over Vieques, Culebra, and the British Virgin Islands today. Tropical storm conditions are expected in Puerto Rico this afternoon and tonight," the NHC said.

Meteorologist Rob Molleda, who works at the Miami-based NHC, told EFE that radar images from San Juan showed that the storm's effects began to be felt in Puerto Rico early Wednesday.

Residents will likely experience "pretty severe" effects, including flooding, Molleda said.

"Swells are expected to increase later today across the US and British Virgin Islands and along the southern coasts of Puerto Rico and Hispaniola, and they could cause life-threatening surf and rip current conditions," the NHC said.

The NHC said Dorian would probably dump heavy rains on eastern Puerto Rico, the Virgin Islands, the northwestern Bahamas and the southeastern United States.

"This rainfall may cause life-threatening flash floods," the NHC said.

Dorian will be the "first significant (storm) impact" for Puerto Rico since Hurricane Maria hit the island in September 2017, killing about 3,000 people, Molleda said.

Police said an 80-year-old man who was trying to prepare his house for the arrival of Dorian became the hurricane's first victim on Wednesday.

The man died when he slipped and fell from the roof of his house in the city of Bayamon, hitting his head on the ground.

In the Dominican Republic, the national emergency management office has alerts in effect for San Pedro de Macoris, La Romana, Hato Mayor, Seibo, Samanand and La Altagracia provinces.

After making its way through the Bahamas, Dorian is forecast to head toward central Florida, but the forecast track "can easily change" because the storm is still so many days away from making landfall, Molleda said. EFE