SAN JUAN, Puerto Rico — Search-and-rescue efforts on this storm-ravaged island redoubled Thursday as residents took stock of the devastation left by Hurricane Maria, which continued to plague the U.S. territory in the form of dangerous flash floods even as its core drifted northwest to deliver a weaker but still punishing blow to the Dominican Republic.

The powerful storm knocked out power to the entire island and felled cellphone towers, leaving many residents unable to call for help or communicate with family members. Downed trees blocked roadways, some of which were turned into fast-flowing, muddy rivers. The obstacles complicated efforts to assess the full scope of damage, though authorities are already estimating that the potential cost could to reach into the billions.

“Today, we’re working on that assessment, evaluating what in terms of money what is the real cost of the aftermath of the hurricane,” said Carlos Mercader, a Washington-based spokesman for Gov. Ricardo Roselló. “But I can tell you, from what I’ve been hearing from the governor, there’s total devastation.”

A more immediate concern for many here, however, is flooding as the trailing bands of Maria continue to deliver waves of heavy rainfall. “Catastrophic flooding is occurring on the island, especially in areas of mountainous terrain, and everyone in Puerto Rico should continue to follow advice from local officials to avoid these life-threatening flooding conditions,” the National Hurricane Center said in its mid-morning advisory.

Some relief organizations, such as Save the Children and Catholic Charities, are holding off operations until they can be certain that conditions on the ground are safe.

Images trickling out of the U.S. territory, home to about 3.5 million Americans, show blown-out windows and roofs peeled off the tops of buildings, the interiors open to the elements. Enormous trees were pulled out by their roots, their branches stripped bare by the hurricane-force winds. Neighbors helped each other clear out downed trees and sweep up piles of broken glass from their businesses.

Maria — now a Category 3 hurricane — was expected to gather some fresh strength over open water before taking aim at the Turks and Caicos Islands, which were battered earlier this month by Hurricane Irma on its deadly path toward Florida.

Maria may spare the U.S. mainland. The current National Hurricane Center forecasts show it veering sharply to the north and spinning up the Atlantic in the corridor between Bermuda and the Atlantic seaboard. But the ultimate path — either closer or farther from the U.S. coast — was still unclear and influenced by weather forces from the remnants of Hurricane Jose now off New England.

Before striking Puerto Rico, Hurricane Maria pummeled parts of the U.S. Virgin Islands, where authorities also continued to arduous task of assessing and clearing out the damage wrought by both Maria and Irma. Kenneth E. Mapp, governor of the territory, on Thursday morning announced an immediate, indefinite curfew on St. Croix, St. John, St. Thomas and Water Island to give space to repair crews.

“Your presence on the roads during the curfew hours will only hamper clean-up efforts, and could delay the distribution of critically needed supplies,” he said in a statement.

It also devastated the island nation of Dominica, where the prime minister said Thursday that at least 15 were confirmed dead and another 20 were missing in the wake of the storm, according to the Associated Press.

President Trump on Thursday acknowledged the likelihood of severe damage to Puerto Rico, describing the U.S. territory as “totally obliterated.” The island is in “very, very, very perilous shape,” Trump told reporters in New York during a meeting with Ukraine President Petro Poroshenko.

It was the first Category 4 storm to strike the island directly since 1932. The devastation, too, is something the island has not seen in generations.

“Months and months and months and months are going to pass before we can recover from this,” Felix Delgado, the mayor of the northern coastal city of Catano, told the Associated Press.

First responders, including a fire-rescue team deployed from Fairfax, Va., had to ride out the storm for hours before emerging to help people late Wednesday. In the meantime, calls to emergency services went in vain. A family in the southern coastal town of Guayama, for example, reportedly pleaded for help as they were trapped in their home with rising water.

In Hato Rey, a San Juan business district, a woman sought assistance as she was experiencing labor pains. “Unfortunately, our staff cannot leave,” Gómez said at the news conference. “They will be rescued later.”

William “Brock” Long, administrator of the Federal Emergency Management Agency, told The Washington Post that rescue and recovery operations are poised to help the U.S. territories — and had significant resources already deployed in the area as a result of Hurricane Irma, which hit the region just days ago.

“Right now we’re in wait-and-see mode,” Long said Wednesday afternoon. “We know that St. Croix took a tremendous hit, and we know obviously Puerto Rico took the brunt of the storm. Once the weather clears and the seas die down, we’ll be in full operation.”

Puerto Rico’s governor, Ricardo Rosselló, ordered a 6 p.m. to 6 a.m. curfew to remain in place at least until Saturday. Late Wednesday, President Trump declared a “major disaster” in Puerto Rico and directed additional federal funds to help in the recovery, a White House statement said.

In a tweet address to Rosselló, Trump wrote Thursday that “we are with you and the people of Puerto Rico.”

Maria was the most violent tropical cyclone to hit Puerto Rico in more than 80 years. It had raked St. Croix hours earlier, just two weeks after that island was the only major land mass in the U.S. Virgin Islands that was spared Hurricane Irma’s wrath. Maria also produced flooding in St. Thomas, an island that Irma hit.

On the French island of Guadeloupe, officials blamed at least two deaths on Maria, and at least two people were missing after a ship went down near the tiny French island of Desirade. At least seven deaths have been reported on the devastated island of Dominica.

Del. Stacey Plaskett, who represents the U.S. Virgin Islands in Washington, said St. Croix had been a staging ground for relief efforts after Hurricane Irma devastated other parts of her district, before Maria’s eye skimmed the edge of St. Croix on Tuesday night as a Category 5 storm with winds of 175 mph.

The damage has yet to be fully assessed, but in a sign of the possible devastation, Plaskett said the roof of the local racetrack blew into the runway of the airport, complicating relief efforts.

The last hurricane to make landfall in Puerto Rico was Georges in 1998. Just one Category 5 hurricane has hit Puerto Rico in recorded history, in 1928.

Puerto Rico’s vulnerability to tropical cyclones has been driven home in the past two weeks as first Irma and then Maria have howled into the Caribbean. The back-to-back nature of the storms has had one minor upside: Some 3,200 federal government staffers, National Guardsmen and other emergency personnel already were in Puerto Rico when Maria approached.


A resident looks at the broken windows of an apartment in Ciudadela complex of Santurce in Puerto Rico. (Dennis M. Rivera Pichardo for The Washington Post)

Late Wednesday, Trump issued a message on Twitter naming the Puerto Rican governor, adding: “We are with you and the people of Puerto Rico. Stay safe! #PRStrong.”

The federal recovery effort, Long said, will attempt to restore power to Puerto Rico and the U.S. Virgin Islands as quickly as possible but in a way that makes the grid less vulnerable to similar disruptions. The power grid, he said, “is a fragile system in both territories. It’s going to be a long and frustrating process to get the power grid up.”

In the San Juan district of Santurce, residents used machetes to cut branches from trees blocking the road. The sidewalks were rendered impassable by downed trees, metal roofing and power lines.

Anton Rosarios, 81, looked over what remained of the front of his wooden house, the walls of which had collapsed, exposing the interior. He said he was hoping that FEMA would show up: “They are the only ones who can help fix this neighborhood. God willing, they will be coming to help us soon.”

The home of his neighbor, Vitin Rodriguez, 55, had lost its roof, and all of his belongings had been ruined by Maria. A tree had fallen and crushed his car, and he said he had no way to check on the status of family members.

Farther down the block, a small crowd gathered at an emergency shelter, as residents checked on friends and neighbors, some of whom had ridden out the storm playing dominoes.

“It’s important to help, to give a life to people who don’t have homes because of the storm,” said Eudalia Sanata, 46, one of the four employees of the shelter. “Look, there are even a few dogs here. Dogs are part of the family, too, and no one wants to leave their family out in the rain.”

Somashekhar reported from Washington. Daniel Cassady in San Juan; Amy Gordon in Vieques, Puerto Rico; and Brian Murphy, Joel Achenbach, Jason Samenow and Angela Fritz in Washington contributed to this report.