CORPUS CHRISTI, Texas -- Hurricane Harvey hit south Texas head-on late Friday, with the Category 4 storm unleashing torrential rain and blazing winds, and leaving thousands without power by Saturday morning.
The powerful eye wall of Harvey reached land by 9 p.m. MDT Friday between Port Aransas and Port O'Connor, Texas, with winds of 130 mph, the National Hurricane Center said.
It is the first Category 4 hurricane to make landfall in the United States since Hurricane Charley in 2004.
Millions of residents along the south Texas coast saw hurricane-force winds that knocked down trees, power poles and signs.
First responders are yet to assess the impact that the extremely powerful hurricane has caused over Texas in the first hours since landfall, but forecasters have said it will be devastating and leave areas "uninhabitable for weeks or months."
Harvey has the "highest potential to kill the most amount of people and cause the most amount of damage," said Brock Long, director of the Federal Emergency Management Agency.
As Harvey deluges Texas, coastal cities could see 13 feet of storm surge and as much as 40 inches of rain by Wednesday.
Joey Walker, 25, works with the Galveston Island Beach Patrol and is riding out the storm from a house on Galveston Island. He posted video of near-whiteout conditions overlooking Stewart Beach.
Houston Mayor Sylvester Turner said anyone not leaving should plan to stay off the roads once the storm starts.
"People need to know, this is not a one-, two-day event and done," Turner said.
The storm will stall and dump rain on south Texas and parts of Louisiana into the middle of next week, forecasters predicted.
Those who stay should "elevate and get into a structure that can withstand potentially Category 3 winds from a hurricane," Long said.
"The bottom line message is, right now, if people have not heeded the warning, again, their window to do so is closing," Long said. "If they refuse to heed the warning, that's on them."
Long said he is "very worried" about storm surge, or "wind-driven water," slamming coastal areas, saying it has the "highest potential to kill the most amount of people and cause the most amount of damage."
President Donald Trump tweeted that he has spoken with the governors of Texas and Louisiana, saying he is "closely monitoring Hurricane Harvey developments and here to assist as needed."
Officials worried Harvey's deluge of rain will drench Texas and the region for several days.
"We could see this storm park for almost five days in some places, and we hear three feet of rain," said Bill Read, the former director of the National Hurricane Center. "That's just going to be a huge problem for these areas."
"The water is going to be the issue," Corpus Christi Mayor Joe McComb said. "We've never had anything like this."
Harvey is also causing concern in New Orleans, where heavy rain could usher in as much as 20 inches of rain through early next week and overwhelm the city's already-compromised drainage system.