WATCH LIVE: Texas Gov. Greg Abbott to address devastation caused by Hurricane Harvey

Click here to watch Governor Abbott’s news conference on Hurricane Harvey

Hurricane Harvey rolled over the Texas Gulf Coast on Saturday, smashing homes and businesses and lashing the shore with wind and rain so intense that drivers were forced off the road because they could not see in front of them.

The fiercest hurricane to hit the U.S. in more than a decade came ashore late Friday about 30 miles (48 kilometers) northeast of Corpus Christi as a mammoth Category 4 storm with 130 mph (209 kph) winds. It weakened overnight to Category 1.

But the storm’s most destructive powers were just beginning. Rainfall that will continue for days could dump more than 40 inches of water and inundate many communities, including dangerously flood-prone Houston, the nation’s fourth-largest city.

“Our focus is shifting to the extreme and potentially historic levels of flooding that we could see,” said Eric Blake, a specialist at the National Hurricane Center in Miami.

No deaths were immediately reported. High winds kept emergency crews out of many places, and authorities said it could be hours before emergency teams are able to fully assess damage.

By dawn, nearly 300,000 consumers were without power in the coastal region, and nearly 20 inches (0.5 meters) of rain had fallen in some places.

The mayor of Rockport, a coastal city of about 10,000 that was directly in the storm’s path, said his community took a blow “right on the nose” that left “widespread devastation,” including homes, businesses and schools that were heavily damaged. Some structures were destroyed.

Mayor Charles “C.J.” Wax told The Weather Channel that the city’s emergency response system had been hampered by the loss of cellphone service and other forms of communication.

About 10 people were taken to the county jail for treatment after the roof of a senior housing complex collapsed, television station KIII reported.

On Friday, Rockport Mayor Pro Tem Patrick Rios offered ominous advice, telling the station that people who chose not to evacuate should mark their arm with a Sharpie pen, implying that the marks would make it easier for rescuers to identify them.

In the storm’s immediate aftermath, the Coast Guard sent two helicopters to try to rescue the crews of three tugboats reported in distress in a channel near Port Aransas.

About 4,500 inmates were evacuated from three state prisons in Brazoria County south of Houston because the nearby Brazos River is rising from Hurricane Harvey’s heavy rain.

By late morning, Harvey’s maximum sustained winds had fallen to about 75 mph (120 kph) and the storm was centered about 25 miles (40 kilometers) west of Victoria, Texas. It was moving north at 2 mph (3 kph), according to the hurricane center.

The system was expected to become tropical storm by Saturday afternoon.

The hurricane posed the first major emergency management test of President Donald Trump’s administration. The president signed a federal disaster declaration for coastal counties Friday night.

Trump commended the head of the Federal Emergency Management Agency for his handling of the storm.

In a tweet Saturday morning addressed to FEMA head Brock Long, Trump said: “You are doing a great job – the world is watching! Be safe.”

In a separate tweet, Trump said he is monitoring the hurricane closely from Camp David. “We are leaving nothing to chance. City, State and Federal Govs. working great together!”

The president also tweeted, “We have fantastic people on the ground, got there long before #Harvey. So far, so good!”

In Corpus Christi, the major city closest to the storm’s center, wind whipped palm trees and stinging sheets of horizontal rain slapped against hotels and office buildings along the seawall as the storm made landfall.

Daybreak revealed downed lamp posts and tree limbs and roof tiles torn off buildings. The city’s marina was nearly unscathed, save an awning ripped from a restaurant entrance and a wooden garbage bin uprooted and thrown.

Along Interstate 45 leaving Galveston, motorists had to stop under bridges to avoid driving in whiteout conditions.

Fueled by warm Gulf of Mexico waters, Harvey grew rapidly, accelerating from a Category 1 early Friday morning to a Category 4 by evening. Its transformation from an ordinary storm to a life-threatening behemoth took only 56 hours, an incredibly fast intensification.

Harvey came ashore as the fiercest hurricane to hit the U.S. in 13 years and the strongest to strike Texas since 1961’s Hurricane Carla, the most powerful Texas hurricane on record.

The storm’s approach sent tens of thousands of people fleeing inland. Families who escaped Rockport were worried about neighbors and whether their homes are still standing.

Johanna Cochran was panicking over whether her house or the McDonald’s where she works survived the storm. She and her boyfriend evacuated to a San Antonio shelter.

Another Rockport resident, Pamela Montes, said she knew many people who stayed behind because “no one felt like it was going to hit.”

Just hours before the projected landfall, the governor and Houston leaders issued conflicting statements on evacuation.

Gov. Greg Abbott urged more people to flee, but Houston authorities told people to remain in their homes and recommended no widespread evacuations.

Houston Mayor Sylvester Turner said there might be a “greater danger” in having people who don’t need to be evacuated on roads that could flood. Harris County Judge Ed Emmett said that because the hurricane was not taking direct aim at Houston, the city’s primary concern was heavy flooding.

“We are not having a hurricane,” said Emmett, the top elected official for the county, which encompasses Houston. “We are having a rain event.”

The last Category 4 storm to hit the U.S. was Hurricane Charley in August 2004 in Florida. Superstorm Sandy, which pummeled New York and New Jersey in 2012, never had the high winds and had lost tropical status by the time it struck. But it was devastating without formally being called a major hurricane.

Harvey is the first significant hurricane to hit Texas since Ike in September 2008 brought winds of 110 mph (177 kph) to the Galveston and Houston areas, inflicting $22 billion in damage.