FREEPORT, Bahamas — Hurricane Dorian unleashed massive flooding across the Bahamas on Monday, pummeling the islands with so much wind and water that authorities urged people to find floatation devices and grab hammers to break out of their attics if necessary.

The fearsome Category 4 storm slowed almost to a standstill as it shredded roofs, hurled cars and forced even rescue crews to take shelter until the onslaught passed.

Officials said they received a “tremendous” number of calls from people in flooded homes. Forecasters warned that Dorian could generate a storm surge as high as 23 feet (7 meters).

Police Chief Samuel Butler urged people to remain calm and share their GPS coordinates, but he said rescue crews had to wait until weather conditions improved.

“We simply cannot get to you,” he told Bahamas radio station ZNS, which shared reports from callers who said some people were stuck on roofs and in attics.

On nearby Abaco Island, Parliament member Renward Wells said he received reports of casualties but officials had not been able to confirm them.

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 midday Monday, the storm’s top sustained winds fell slightly to 155 mph (250 kph). It was crawling along Grand Bahama Island at just 1 mph (2 kph).

The water reached roofs and the tops of palm trees. One woman filmed water 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 heavy flooding.

Parliament member Darren Henfield described the damage as “catastrophic” and said officials did not have information on what happened in nearby cays. “We are in search-and-recovery mode. … Continue to pray for us.”

A spokesman for Bahamas Power and Light told ZNS that there was a blackout in New Providence, the archipelago’s most populous island. He said the company’s office in Abaco island was flattened.

“The reports out of Abaco as everyone knows,” spokesman Quincy Parker said, pausing for a deep sigh, “were not good.”

Most people went to shelters as the storm neared. Tourist hotels shut down, and residents boarded up their homes. Many people were expected to be left homeless.

On Sunday, Dorian’s maximum sustained winds reached 185 mph (297 kph), with gusts up to 220 mph (354 kph), tying the record for the most powerful Atlantic hurricane to ever make landfall. That equaled the Labor Day hurricane of 1935, before storms were named. The only recorded storm that was more powerful was Hurricane Allen in 1980, with 190 mph (305 kph) winds, though it did not make landfall at that strength.

The Bahamas archipelago is no stranger to hurricanes. Homes are required to have metal reinforcements for roof beams to withstand winds into the upper limits of a Category 4 hurricane, and compliance is generally tight for those who can afford it. Risks are higher in poorer neighborhoods that have wooden homes in low-lying areas.

Forecasters said Dorian was likely to begin pulling away from the Bahamas early Tuesday and curving to the northeast parallel to the southeastern coast of the U.S. The system is expected to spin 40 to 50 miles (64 to 80 kilometers) off Florida, with hurricane-force wind speeds extending about 35 miles (56 kilometers) to the west.

An advisory from the hurricane center warned that Florida’s east-central coast could see a brief tornado sometime Monday afternoon or evening.

South Carolina Gov. Henry McMaster issued an order Sunday for the mandatory evacuation of his state’s entire coast. The order, which covers about 830,000 people, was to take effect at noon Monday, at which point state troopers were to make all lanes on major coastal highways one-way heading inland.

“We can’t make everybody happy, but we believe we can keep everyone alive,” McMaster said.

A few hours later, Georgia’s governor, Brian Kemp, ordered mandatory evacuations for that state’s Atlantic coast, also starting at midday Monday.

Authorities in Florida ordered mandatory evacuations in some vulnerable coastal areas. North Carolina Gov. Roy Cooper warned his state that it could see heavy rain, winds and floods later in the week.

The hurricane center issued a hurricane watch for Florida’s East Coast from Deerfield Beach north to Altamaha Sound in Georgia. A storm surge watch was extended northward along the Georgia coast to the Savannah River. Lake Okeechobee was under a tropical storm watch.

Weekend traffic was light in Florida despite the many evacuation orders, unlike during the chaotic run-up to Hurricane Irma in 2017, when the unusually broad storm menaced the entire state.