Hurricane Maria slammed into the Caribbean island of Dominica as a Category 5 storm with "merciless" 160 mph winds Monday night, and the storm, deemed "potentially catastrophic" by the National Hurricane Center, is now headed for the Virgin Islands and Puerto Rico.

Maria is expected to move over the northeastern Caribbean Sea today and is forecast to "remain an extremely dangerous category 4 or 5 hurricane" as it approaches the Virgin Islands and Puerto Rico tonight and Wednesday, the National Hurricane Center said.

Most models are forecasting Maria will stay away from Florida and the United States mainland.

Puerto Rico Gov. Ricardo Rossello said the island is facing "an unprecedented situation" as residents brace for their second major hurricane just two weeks after Irma tore through the U.S. territory, killing at least three.

Rossello said tropical storm force winds are expected today and hurricane force winds are expected throughout Wednesday. Residents should expect to be without power for a period of time, but the length depends on the damage to the island, he noted.

As Maria hit Dominica Monday night, Dominica Prime Minister Roosevelt Skerrit published a series of dire Facebook posts, calling the 160 mph winds "merciless."

"We do not know what is happening outside. We not dare look out ... we pray for its end!" Skerrit wrote.

Maria was the first Category 5 hurricane to made landfall on Dominica; before Monday the strongest hurricane to hit Dominica was Hurricane David, a Category 4 in 1979.

Dominica was "shut down" as the storm approached, said Anil Etienne, a spokesperson for Dominica’s Office of Disaster Management. Etienne told ABC News officials were worried about flooding in low-lying areas and opened about 146 shelters.

ABC NEWS