The core of "extremely dangerous" Hurricane Maria charged closer to Puerto Rico early Wednesday, slamming smaller Caribbean islands along the way.

Maria had top sustained winds of 155 mph, and was located about 50 miles southeast of San Juan, the National Hurricane Center reported in its 5 a.m. ET Wednesday advisory.

The major hurricane was moving to the west-northwest at 10 mph, and was "expected to reach southeastern Puerto Rico this morning," according to the NHC.

"Conditions will continue to deteriorate across the U.S. and British Virgin Islands, with the worst conditions there early Wednesday morning," Fox News Senior Meteorologist Janice Dean said Tuesday. "Puerto Rico is forecast to take a direct hit from this major hurricane on Wednesday, with the worst conditions from late Wednesday morning through Wednesday afternoon."

Early Wednesday, Maria passed west of St. Croix in the U.S. Virgin Islands, as winds on the island reached about 90 mph, Reuters reported. Many of the island's residents moved to shelters Tuesday afternoon.

U.S. Virgin Islands Gov. Kenneth Mapp minced no words in warning residents to seek cover, Reuters reported.

“You lose your life the moment you start thinking about how to save a few bucks to stop something from crashing or burning or falling apart,” he said. “The only thing that matters is the safety of your family, and your children, and yourself. The rest of the stuff, forget it.”

Officials in Puerto Rico also issued blunt warnings.

"You have to evacuate. Otherwise, you're going to die," said Hector Pesquera, Puerto Rico’s public safety commissioner. "I don't know how to make this any clearer."

The island’s governor warned that the storm could hit “with a force and violence that we haven’t seen for several generations.”

"We're going to lose a lot of infrastructure in Puerto Rico," Gov. Ricardo Rossello said, adding that an island-wide power outage and communication blackout could likely last for days. "We're going to have to rebuild."

The warnings from Puerto Rican officials came after Maria’s path moved through Dominica, which left “mind-boggling devastation” on the island.

Dominica Prime Minister Roosevelt Skeritt posted to Facebook that "initial reports are of widespread devastation." Skeritt said he feared there would be deaths due to rain-fed landslides.

He said even his own house had lost its roof, adding "I am at the complete mercy of the hurricane. House is flooding." Seven minutes later, Skeritt reported he’d been rescued.

Maria's eye roared over the island late Monday night before the storm briefly dropped to Category 4 strength early Tuesday. But it quickly resumed its extremely dangerous Category 5 status.

Fierce winds and rain lashed mountainous Dominica for hours. A police official on the island, Inspector Pellam Jno Baptiste, said late Monday night there were no immediate reports of casualties but it was too dangerous for officers to check many locations.

"Where we are, we can't move," he said in a brief phone interview with the Associated Press while hunkered down against the region's second Category 5 hurricane this month.

The government of Trinidad and Tobago said Tuesday it was mobilizing to send assistance to Dominica in response to Hurricane Maria.

"It is envisaged that as soon as it is safe, a National Helicopter Services Limited helicopter will be sent to Dominica with Trinidad and Tobago Defense Force personnel," the government posted to Facebook. "The Trinidad and Tobago Coast Guard is also preparing to send a supply vessel and to take Defense Force personnel as well as supplies up to Dominica.”

Officials in Guadeloupe said the French island near Dominica probably would experience heavy flooding and warned many communities could be submerged. In nearby Martinique, authorities ordered people to remain indoors and said they should be prepared for power outages and disruption in the water supply.

Guadeloupe prefect Eric Maire said up to 16 inches of rain was forecast in some parts of the island, and storm surge could also flood low-lying coastal areas.

"We've already got some early information of flooding, flooded houses and submerged roads," Maire said in a video posted to Twitter. Officials said one person was killed in Guadeloupe after they were hit by a falling tree. Two additional people were reported missing after their ship sank off Desirade, the easternmost island in the French territory's archipelago.

At least 80,000 households in Guadeloupe and at least 70,000 households in Martinique are without power, France's Interior Minister Gerard Collomb said Tuesday.

St. Thomas and St. John are still recovering from a direct hit by Hurricane Irma, which did extensive damage and caused four deaths on the two islands. Barry University said it chartered a private plane to carry students and staff from its St. Croix facility to Florida in preparation for Maria. It said 72 people connected to Barry's physician assistant program and a few pets were on Monday's evacuation flight.

On the British Virgin Islands, the local government issued a curfew in advance of the storm, Sky News reported.

"While Hurricane Maria may not be as strong as Hurricane Irma, our present reality is also very different," Orlando Smith, the premier of the self-governing British territory, said in a statement. "Effects such as potential flooding and high winds that can turn debris into dangerous projectiles can have a greater and more treacherous impact for us."

British Prime Minister Theresa May said during her visit to New York for the United Nations General Assembly the government was doing "everything possible" to help overseas territories like the British Virgin Islands.

"We had been tracking the path of Hurricane Maria and are in a strong position to respond and get support where and when we need it," she said. "We're working closely with the authorities in the territories and British support is on the ground already with over 1,300 military troops and Royal Navy assets in the region."

In a tweet Tuesday night, President Donald Trump said: "Puerto Rico being hit hard by new monster Hurricane. Be careful, our hearts are with you- will be there to help!"

Authorities in the U.S. territory of Puerto Rico, which faced the possibility of a direct hit, warned people in wooden or flimsy homes to find safe shelter before the storm's expected arrival there Wednesday.

Nearly 70,000 people were still without power in Puerto Rico following their earlier brush with Irma and nearly 200 remained in shelters as Maria approached.

Gov. Ricardo Rossello said Puerto Rico had 500 shelters capable of taking in up to 133,000 people in a worst-case scenario. He also said the Federal Emergency Management Agency was ready to bring drinking water and would help restore power immediately after the storm, which could hit as a Category 5.

"That is catastrophic in every way," said Roberto Garcia with the National Weather Service in San Juan. "People have to act, and they have to act now. They can no longer wait for a miracle."

The Associated Press contributed to this report.