FREEPORT, Bahamas — Hurricane Dorian hovered over the Bahamas on Monday, pummeling the islands with a fearsome Category 4 assault that shredded roofs, hurled cars and forced even rescue crews to take shelter until the onslaught passes.

The storm’s top sustained winds fell slightly to 155 mph (250 kph), and its westward movement slowed almost to a standstill. The system crawled along Grand Bahama Island at just 1 mph (2 kph) and was expected to generate a storm surge of 18 to 23 feet (6 to 7 meters).

“We need you to bunker down,” Kwasi Thompson, minister of state for Grand Bahama, warned people. “It’s going to be another 10-12 hours that we’re going to be bombarded with this.”

Thompson and other officials said they received distress calls about rising floodwaters, but rescuers could not go out in the violent conditions.

“They are ready to get into those areas as soon as the weather subsides,” he said.

Meanwhile in the United States, the National Hurricane Center extended watches and warnings across the Florida and Georgia coasts. Forecasters expected Dorian to stay just off shore, but meteorologist Daniel Brown cautioned that “only a small deviation” could draw the storm’s dangerous core toward land.

By late Monday morning, the water had already reached roofs and the tops of palm trees in Grand Bahama. One woman filmed floodwaters lapping at the stairs of her home’s second floor.

In Freeport, Dave Mackey recorded video showing water and floating debris surging around his house as the wind shrieked outside.

“Our house is 15 feet up, and right now where that water is is about 8 feet. So we’re pretty concerned right now because we’re not at high tide,” said Mackey, who shared the video with The Associated Press. “Our garage door has already come off. … Once we come out of it with our lives, we’re happy.”

On Sunday, Dorian churned over Abaco Island with battering winds and surf and unleashed heavy flooding as people called radio stations and sent desperate messages on social media to find loved ones.

“We received catastrophic damage here in Abaco,” Parliament member Darren Henfield told reporters. He said officials did not have information yet on what happened in nearby cays. “We are in search-and-recovery mode. … Continue to pray for us.”

Information began emerging from other affected islands, with Bahamas Power and Light spokesman Quincy Parker telling radio station ZNS that there was a total blackout in New Providence, the archipelago’s most populous island. He also said the company’s office in Abaco island was flattened by the storm.