CORPUS CHRISTI — Hurricane Harvey made landfall as a Category 4 storm in Texas late Friday, bringing with it 130-mph winds and unleashing flash floods, storm surges and up to three feet of rain.

Harvey is the first major hurricane — classified as Category 3 or above — to hit the USA since Hurricane Wilma in 2005.

"This is going to be a very major disaster," said Gov. Greg Abbott, who declared a State of Disaster for 30 counties and requested 700 National Guard members to be activated.

He warned of record-setting flooding in multiple regions of the state and urged people to get out of harm's way. “You don’t want to put yourself in a situation where you could be subject to a search and rescue.”

Some forecasts are calling for as much as a mind-boggling 60 inches (that's five feet) of rain from Harvey.

As many as 1.25 million Texans could lose power from the storm, according to forecast models at Texas A&M University.

With some 700,000 people living in the hurricane warning zone — roughly half of them around Corpus Christi — traffic backups tied up heavily traveled roads such as Interstate 37 as people move toward San Antonio and other inland locations.

Fueled by the warm Gulf waters, Harvey jumped within hours from a Category 2 to Category 4 hurricane on Friday. As of 4 p.m. CDT, the center was located 60 miles east-southeast of Corpus Christi, Texas. The storm had winds of at least 125 mph and was moving to the northwest at 10 mph.

The National Weather Service warned that Harvey could linger for days and even spin back offshore to regenerate in the Gulf before heading toward Louisiana.

"The flooding will be catastrophic and life-threatening," weather service director Louis Uccellini said in a statement. "The economic impact will likely be devastating."

Locations may be uninhabitable for weeks or months, the weather service in Corpus Christi said.

It would be the strongest hurricane to hit the U.S. in 12 years. A major hurricane is one that's a Category 3 or above on the Saffir-Simpson scale of hurricane intensity.

The last Category 3 storm to hit the U.S. was Hurricane Wilma, which barreled into Florida in Oct. 2005.

President Trump weighed in on the storm, tweeting that he is "closely monitoring" and "here to assist as needed."

All seven Texas counties on the coast from Corpus Christi to the western end of Galveston Island have ordered the mandatory evacuations of tens of thousands of residents from low-lying areas.

Most people heeded the warnings to clear out of exposed or low-lying areas. In Bloomington, Texas, more than 60 residents checked into a Red Cross shelter in this city 78 miles north of Corpus Christi and square in the path of the hurricane.

Inside a high school basketball stadium, residents on Friday lingered on cots, stockpiled blankets or checked on relatives via cell phones.

For Michelle Pettis, 24, the retreat to the shelter was an easy decision: The trailer home in which she lives with her 4-year-old daughter, Aubrey Cardenas, and 1-year-old son, Ethan Cardenas, wasn't stable enough and her mother was in Florida on vacation.

She gathered pictures, important documents, blankets and toys for the kids and moved into the shelter Thursday night.

More so than strong winds, its Harvey's pounding rains that motivated her to move, she said.

"Flooding is what scares me the most," Pettis said. "We don't know how long it's going to last or what it's going to do."

Thomas Westgate, a Red Cross supervisor at the shelter, said the gym is equipped to house about 300 residents. Residents have been trickling in all day, as they realize the enormity and intensity of the storm heading their way, he said.

William Foster, 55, and Yolanda Guajardo, 47, who share a trailer home in Placido, Texas, initially disagreed about how best to ride out Harvey: He wanted to stay home, she wanted to evacuate to a shelter.

Guajardo won. On Friday, the two shared cigarettes outside the Red Cross shelter in Bloomington, where they moved into Thursday night.

"I'm expecting thunder, lightning, things flying around," she said. "I'm afraid."

Voluntary evacuations have been urged for Corpus Christi and for the Bolivar Peninsula, where many homes were washed away by the storm surge of Hurricane Ike in 2008. Corpus Christi city councilman Greg Smith, who represents Padre Island, said residents who stay could be stranded for days if the storm surge surpasses 10 feet.

State transportation officials were considering when to turn all evacuation routes from coastal areas into one-way traffic arteries headed inland.

John Barton, a former deputy executive director of the Texas Department of Transportation, predicted state officials will do this before the storm hits, but said timing and determining where to use it are the key factors. Storms change paths and if contraflow starts too early, supplies such as extra gasoline needed to support impacted areas can’t get in, he said.

Outside Tabernacle of Praise Church, Pastor Freddy Naranjo and a small band of men were boarding up the front entrance of the beige building.

Amid the sharp, shrill grinds of an electric saw, Naranjo said he and his group spent about two hours at Home Depot for supplies the night before. They secured his home, slept about three hours and began work securing the church, he said.

Naranjo plans to stay in town and return to the church as soon as possible after the storm’s passage.

“We’re hoping to have church Sunday,” he said. “You know us. We live for that.”

Corpus Christi Mayor Joe McComb and county officials stopped short of ordering a mandatory evacuation for the city, but they said residents who stay are risking their lives.

Not everyone was headed for higher ground. Kendra Holbert, 40, said she was staying put with her mother, two sisters and two sons — all in a Corpus Christi apartment.

The family had stocked up on water, canned goods, flashlights, batteries and peanut butter and jelly. Holbert was visiting a Stripes gas station Friday morning for last-minute gas and tacos.

Like other residents, she said she was most worried about Harvey lingering in the area for days.

"As long as we're together," she said, "we'll be alright."

One of the toughest tasks after Hurricane Harvey trudges ashore will fall to Jeff Saunders, director of Texas Task Force 1, one of 28 federal teams under FEMA's National Urban Search and Rescue System.

In a typical hurricane that hits a coast and keeps moving, Saunders would wait until winds died down to weak tropical storm strength before dispatching his teams to help local law enforcement rescue residents off rooftops or from flood-ravaged homes.

But since Harvey is forecast to stall over the region for several days, he may not have that luxury, Saunders said.

Nine water squads are spread out across the Texas coast, waiting on orders to go in.

"We're definitely going to be operating in a hazardous environment the entire time," he said.

The National Weather Service in Houston said some areas could see dangerous and life-threatening flash flooding.

CoreLogic, a company based in Irvine, Calif., that conducts global property analysis, estimates that almost 233,000 homes along the Texas coast are at risk due to Hurricane Harvey and that the potential reconstruction would total almost $40 billion.

The National Hurricane Center warns that certain "locations may be uninhabitable for weeks or months."

The hurricane warning covers an area from Port Mansfield (near the Mexican border) to Sargent, which is 70 miles southwest of Galveston.

Contributing: Julie Garcia and Matt Woolbright, Corpus Christi Caller-Times; Gregory Korte, USA TODAY; Melanie Eversley, USA TODAY, Associated Press

Stanglin and Rice reported from McLean, Va.