NBC News – More than 300,000 people were in the dark Saturday after Hurricane Harvey smashed into Texas, downing power lines and bringing prolonged rainfall that was expected to cause “catastrophic flooding.”

It made landfall near Corpus Christi as a Category 4 storm, with maximum sustained winds of 130 mph, and weakened as it moved slowly inland to become a Category 1 by 6 a.m. ET.

While the winds eased to 90 mph, forecasters cautioned torrential rain would still be a major threat.

The National Hurricane Center warned of 12-foot storm surges and up to 40 inches of rain in some areas through Wednesday, with “catastrophic flooding expected over the next few days.”

As the storm hammered the Texas coast, it caused problems on land and in the sea. In the Lydia Ann Channel near Port Aransas, Texas, three tugboats issued mayday calls, the Coast Guard said Saturday morning.

Coast Guard Air Station Corpus Christi launched two MH-65 Dolphin helicopter aircrews to rescue tugboats Belle Chase, Sandy Point, and Sabine Pass, officials said.

The number of power outages, meanwhile, kept increasing. More than 300,000 customers throughout Texas had no electricity, according to the Electric Reliability Council of Texas.

Gov. Greg Abbott warned Texans on Friday that the outages could persist for days.

“If you don’t get out, you could be in the area without power, without water, without necessities for at least a week, if not longer,” Abbott said Friday afternoon.

As daylight broke Saturday, the effects of the hurricane started to become clear.

Corpus Christi Mayor Joe McComb said early Saturday that “horrific” winds had caused “a tremendous amount of damage” in the city and surrounding areas.

He said the storm had cut power to the city’s water treatment plant, meaning residents needed boil water for drinking — but that’s not an option for everyone.

“Many people don’t have electricity so that’s going to create an issue,” he told TODAY. He said power had been cut to his own home overnight.

“I’m waiting to get a little sunlight and the opportunity to get to someplace I can get some power,” he said.

“Sinton community please try to refrain from leaving your house. There are a lot of trees down and low power lines. Also city water is out and this means once they find [the] problem and restore it, we will be in a water boil advisory,” the Sinton Police Department said in a Facebook post.

In Rockport, a city on the coast of Aransas Bay northeast of Corpus Christi, many structures were damaged. City Manager Kevin Carruth said a tree fell on a mobile home Friday, trapping a family inside, but rescuers had to be pulled due to safety concerns and it was unclear if there were any injuries.

Elsewhere in Rockport, multiple people at a senior living home were taken to a nearby jail for treatment after a roof caved in, according to The Associated Press.

The damage was widespread — but officials couldn’t say how serious it would end up being.

“All of our utilities are disrupted,” Rockport Mayor Charles J. Wax told MSNBC. “I have not been in touch with anybody outside of my own team.”

Houston, about 200 miles north of Rockport, was just beginning to feel the effects of Harvey’s outer bands Saturday morning. The National Weather Service issued flash flood warnings, and Houston was put under a tornado watch.

In San Antonio, which welcomed evacuees by the hundreds, rain and wind were picking up.

“We are asking our own residents tho to keep clear of the streets so we can make sure to get the evacuees in,” San Antonio Mayor Ron Nirenberg told MSNBC. “But the conditions are deteriorating.”

The hurricane, moving northwest, is expected to slow down and linger over southeastern Texas through the middle of next week, the hurricane center said.

President Donald Trump signed a disaster declaration late Friday “which unleashes the full force of government help,” he tweeted. The declaration allows federal funding to help stricken areas.

On Saturday morning, Trump tweeted that he was closely monitoring the storm from Camp David. “We are leaving nothing to chance. City, State and Federal Govs. working great together!” he wrote.

He also praised Federal Emergency Management Administrator Brock Long for “a great job.”

The last time a major hurricane struck Texas was in 2008, when Hurricane Ike hit Galveston as a Category 2 hurricane. Ike caused an estimated $22 billion in damage.